THE LESSON LIBRARY / CHEMISTRY
Chemistry, explored.
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Chains, Branches and Rings
Take four carbon atoms and join them. You can line them up in a row, hang one off the middle of a three-carbon row, or close them into a square ring. Each arrangement is a…
Explore lesson ChemistryLessonChair Transition States in [3,3] Shifts
A [3,3] rearrangement can create a new σ bond and move double bonds with high stereochemical order. Its six-atom transition-state array can fold into a chair-like or boat-like…
Explore lesson ChemistryLessonChanges in Everyday Life
You do not need a laboratory to see physical and chemical changes: your kitchen, garden and street are full of them. Ice melts in a drink, bread rises and browns in the oven, an…
Explore lesson ChemistryLessonChanges of State Are Physical Changes
Melt some ice and you get water. Freeze the water and you get ice again. Boil it and it becomes steam, which condenses back into water on a cold window. Through all these changes…
Explore lesson ChemistryLessonChanges of State as Physical Changes
On a cold morning, water may exist as ice on a windscreen, liquid in a puddle and vapour in the air, all at the same time. Changing between these states is one of the most common…
Explore lesson ChemistryLessonChanges of State: An Overview
An ice cube melts in a drink, a puddle dries up in the sun, a bathroom mirror mists over and frost appears on a car windscreen on a cold morning. Each of these is a change of…
Explore lesson ChemistryLessonChanging Markovnikov to Anti-Markovnikov Products
An unsymmetrical alkene can produce different positional products depending on how H and another group add across C=C. Acid hydration commonly places OH on the more substituted…
Explore lesson ChemistryLessonCharacterising Colloids: Light Scattering and Electrophoresis
A colloidal liquid can look uniform while containing a broad mixture of particle sizes and aggregates. Dynamic light scattering, DLS, follows how quickly scattered light…
Explore lesson ChemistryLessonCharacterising Solids
A sample labelled “the target oxide” may actually contain two crystalline phases, amorphous residue, pores and a surface with altered oxidation state. Characterisation tests…
Explore lesson ChemistryLessonCharacterizing Energy Materials
A battery cell that loses capacity and a solar cell that loses power both give a clear performance signal, but neither signal identifies the damaged component. Energy materials…
Explore lesson ChemistryLessonCharacters and Reducible Representations
Writing a matrix for every operation becomes cumbersome when a molecule has many atomic orbitals or displacement coordinates. The trace of each matrix, called its character…
Explore lesson ChemistryLessonCharge and Stability of Colloids
Many sols remain dispersed because their particles repel one another when close enough to collide. The repulsion often comes from charged surfaces and surrounding ions.…
Explore lesson ChemistryLessonCharge Balance in Aqueous Equilibrium
A bulk aqueous solution cannot retain a large net electrical charge. Its positive and negative charge equivalents balance, even though individual ion concentrations need not be…
Explore lesson ChemistryLessonCharge Balance in Aqueous Mixtures
A bulk aqueous solution is electrically neutral even when it contains many charged particles. The positive and negative charges balance in aggregate; the concentrations of…
Explore lesson ChemistryLessonCharge Balance in Aqueous Systems
A beaker of salt solution does not give you an electric shock, and it does not repel a charged rod. Solutions are electrically neutral. That simple observation becomes a precise…
Explore lesson ChemistryLessonCharge-Transfer Spectra
Some coordination compounds have intense colours even with no conventional d–d transition. Their absorption can move electron density between ligand and metal rather than merely…
Explore lesson ChemistryLessonCharge, Current and Time — Electricity and Chemistry
Chemical product amounts in electrolysis depend on how much charge passes, not merely on whether a cell was switched on. At constant current, charge Q equals current I multiplied…
Explore lesson ChemistryLessonCharge, Current and Time — Electrochemistry
Electrolysis problems often provide current and time instead of charge directly. Since one ampere is one coulomb per second, constant-current charge is Q = It. This charge…
Explore lesson ChemistryLessonCharges of Subatomic Particles
The plus and minus signs in atomic diagrams stand for measurable electrical properties. They can be used as relative counting units or converted into coulombs. Learning to move…
Explore lesson ChemistryLessonCharles's Law at Fixed Pressure
When a fixed amount of gas warms under a movable boundary that keeps pressure approximately constant, it expands. Charles's law gives the ideal relationship: volume is directly…
Explore lesson ChemistryLessonChecking and Simplifying Coefficients
Finding coefficients is only part of balancing. A final audit catches quiet mistakes: an oxygen count changed while hydrogen was being fixed, a bracket was not multiplied, or a…
Explore lesson ChemistryLessonChecking Answers for Reasonableness
An answer can pass through a calculator flawlessly and still be chemically unreasonable. Before accepting it, compare the sample with one mole's mass, check whether a particle…
Explore lesson ChemistryLessonChecking Answers with Units
A calculator never argues. If you type the numbers in the wrong order, it will happily give you a precise-looking answer that is completely wrong. Units are your first line of…
Explore lesson ChemistryLessonChecking Balanced Redox Equations
A redox equation can look convincing and still be wrong. Three independent questions catch most errors: Does every element have the same atom count on both sides? Is total…
Explore lesson ChemistryLessonChecking Lewis Structures Systematically
A Lewis structure can look neat and still be wrong. A reliable check asks several separate questions: Are the correct atoms connected? Is the total electron count exact? Do local…
Explore lesson ChemistryLessonChecking Mass Conservation in a Balanced Equation
Balanced equations conserve each element, so they also conserve total mass. We can check this numerically by adding the relative masses of all reactant formula units and…
Explore lesson ChemistryLessonChecking Purity and Identity
After purification, a clean-looking product is not automatically the intended pure compound. Melting and boiling behaviour, TLC or other chromatography, and structural…
Explore lesson ChemistryLessonChelate Effect
Multidentate ligands often bind a metal more strongly overall than an equivalent collection of separate one-site ligands. This is called the chelate effect. It is a thermodynamic…
Explore lesson ChemistryLessonCheletropic Reactions
Ordinary cycloadditions join the ends of two multi-atom components. A cheletropic reaction is a special case in which both new σ bonds to a conjugated substrate attach to a…
Explore lesson ChemistryCollectionChemical and Statistical Thermodynamics I
Study Chemical and Statistical Thermodynamics I with 60 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonChemical and Statistical Thermodynamics: Unit Review
This unit connects the behaviour of individual molecules to phase diagrams used in laboratories and industry. Partition functions encode accessible microscopic states…
Explore lesson ChemistryLessonChemical Behaviour of Metals and Non-metals
Physical properties tell you how an element looks and handles, but chemistry is about how elements react. Here too, metals and non-metals behave in opposite ways. Metal atoms…
Explore lesson ChemistryCollectionChemical Bonding and Molecular Structure
Study Chemical Bonding and Molecular Structure with 70 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonChemical Bonding and Molecular Structure Review
Chemical bonding is not one diagram. Ionic-lattice models, Lewis structures, VSEPR, hybrid orbitals and molecular orbitals each highlight different evidence. A strong review…
Explore lesson ChemistryCollectionChemical Bonding: Ionic and Covalent
Study Chemical Bonding: Ionic and Covalent with 60 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonChemical Bonding: Unit Review
Chemical bonding connects electron arrangements with formulas, structures and material properties. The unit's most important habit is to move carefully between these levels. An…
Explore lesson ChemistryLessonChemical Changes
A shiny strip of magnesium ribbon, touched by a flame, burns with a dazzling white light and leaves behind a crumbly white powder. The powder is not magnesium: it does not shine…
Explore lesson ChemistryLessonChemical Data Provenance
A concentration number without a sample identity or preparation history is difficult to trust or reuse. Even a correct instrument calculation can be assigned to the wrong vial or…
Explore lesson ChemistryCollectionChemical Equations and Balancing
Study Chemical Equations and Balancing with 50 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonChemical Equations and Balancing: Unit Review
This unit turns descriptions of reactions into precise chemical shorthand. A formula says which atoms belong to each substance; a coefficient says how many of those units take…
Explore lesson ChemistryLessonChemical Equilibrium Formulae
An equilibrium formula is built from a balanced reaction. Its quotient compares product and reactant activities with exponents equal to stoichiometric coefficients. The same…
Explore lesson ChemistryLessonChemical Equilibrium Mixed Problems
Mixed equilibrium problems test whether the right question is asked at each stage. A disturbance can change the current quotient, the direction of adjustment, and the final…
Explore lesson ChemistryLessonChemical Exchange on the NMR Timescale
Molecules can interconvert between environments while an NMR instrument observes them. A proton may move between conformers, a ligand may bind and unbind, or two sites may…
Explore lesson ChemistryLessonChemical Formulae: What They Tell Us
A chemical formula is chemistry's shorthand. In just a few characters, such as H₂O, CO₂ or NaCl, it tells a chemist anywhere in the world exactly which substance is meant. A…
Explore lesson ChemistryCollectionChemical Kinetics
Study Chemical Kinetics with 35 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonChemical Kinetics: Unit Review
Chemical kinetics connects observable concentration change with molecular pathways. The central discipline is to keep separate what the balanced equation tells us, what…
Explore lesson ChemistryLessonChemical Potential and Reaction Equilibrium
A reaction changes several species amounts in fixed stoichiometric proportions. Chemical potential tells how Gibbs energy responds to each amount change; adding those responses…
Explore lesson ChemistryLessonChemical Potential and Spontaneous Matter Flow
A gas diffuses, a solute crosses a membrane, and a liquid evaporates because moving material can lower the appropriate thermodynamic potential. At constant temperature and…
Explore lesson ChemistryLessonChemical Potential from Particle Exchange
Chemical potential is often introduced as partial molar Gibbs energy. A particle-exchange viewpoint makes its meaning more concrete: it is the free-energy cost of adding material…
Explore lesson ChemistryLessonChemical Potential of an Ideal Gas
Compressing an ideal gas changes its tendency to move, mix and react even when temperature stays constant. Chemical potential measures that tendency. For an ideal gas, its…
Explore lesson ChemistryLessonChemical Potential of Ions in Solution
Concentration counts dissolved particles, but it does not by itself express the free-energy tendency of an ion to move or react. Neighboring ions alter that tendency through…
Explore lesson ChemistryLessonChemical Potential: Worked Problems
Chemical-potential problems often combine several formulas that look similar but apply to different species and reference states. An ideal gas uses a partial-pressure ratio, an…
Explore lesson ChemistryLessonChemical Properties of Isotopes
Isotopes of an element normally form the same broad kinds of compounds. This follows from their shared nuclear charge and, when neutral, their shared electron count. Their…
Explore lesson ChemistryLessonChemical Quantities and Measurement
Chemistry calculations begin with measured quantities, but a number alone is not an answer. “Five” might mean grams, millilitres, moles or molecules. A complete statement gives a…
Explore lesson ChemistryLessonChemical Reactions as Networks
A single reaction arrow hides much of what can happen in a flask, catalyst or atmosphere. Reactants can form intermediates, branch into products and cycle back through reversible…
Explore lesson ChemistryLessonChemical Shift and the δ Scale
Protons in different chemical environments absorb at slightly different radio frequencies. The trouble is that the actual frequencies depend on the magnet: the same proton in…
Explore lesson ChemistryLessonChemical Tests for Water
Many colourless liquids look just like water: ethanol, some salt solutions and various oils. How can a chemist tell whether a liquid contains water without tasting it (which is…
Explore lesson ChemistryLessonChemiosmosis and the Proton-Motive Force
The electron transport chain moves electrons downhill in free energy, yet ATP synthase is a separate protein. How does one process power the other without passing a reactive…
Explore lesson ChemistryLessonChemistry All Around Us
You do not need a laboratory to meet chemistry. Every morning you use dozens of chemical products and take part in hundreds of chemical reactions before you even leave the house.…
Explore lesson ChemistryLessonChemistry and Society
Much of modern life depends on chemistry. People today live longer, eat more reliably and have more energy available than at any time in history, and chemistry is a major reason…
Explore lesson ChemistryLessonChemistry and the Environment
The same chemistry that gives us fuels, fertilisers and plastics can harm air, water and soil when substances end up in the wrong place or in the wrong amounts. Understanding…
Explore lesson ChemistryLessonChemistry Glossary: How to Use Terms
A chemistry glossary is a tool for reasoning, not a list of words to memorize without context. The same everyday word may carry a narrower chemical meaning, and the same letter…
Explore lesson ChemistryLessonChemistry Glossary: Unit Review
The glossary is complete when its words help solve a problem, not when its entries have been memorized. Across the course, a sample may be a mixture yet one phase; an equation…
Explore lesson ChemistryLessonChemists and What They Do
When you hear the word "chemist", you might picture someone in a white coat pouring coloured liquids. Some chemists do work like that, but chemists also design medicines on…
Explore lesson ChemistryLessonChemoselectivity and Protecting Groups
A route can be sound for an isolated functional group and fail in a molecule containing several reactive sites. A reagent meant to transform one alcohol may react with another; a…
Explore lesson ChemistryLessonChemoselectivity and Regioselectivity
A reagent can encounter more than one possible partner in a complex molecule. Choosing one functional-group type over another is chemoselectivity; choosing one position within a…
Explore lesson ChemistryLessonChemoselectivity in Multi-Step Routes
A multifunctional molecule gives a reagent more than one possible place to react. Chemoselectivity asks whether the desired functional group changes while another remains intact.…
Explore lesson ChemistryLessonChemoselectivity, Regioselectivity and Stereoselectivity — Catalyst Design and Comparison
“Selective” is ambiguous until the alternatives are named. A molecular catalyst can choose which functional group reacts, which position on a molecule is modified and which…
Explore lesson ChemistryLessonChemoselectivity, Regioselectivity and Stereoselectivity — Organometallic Chemistry and Catalysis
A catalyst that makes a mixture of products is rarely useful. The real power of organometallic catalysis lies in steering a reaction toward one functional group, one position and…
Explore lesson ChemistryLessonChina Rose and Flower Petal Indicators
Walk through a garden in a warm country and you will often see large, bright red hibiscus flowers, known in India as the China rose. These petals are not only beautiful: they…
Explore lesson ChemistryLessonChiral Pool, Auxiliaries and Asymmetric Catalysis
If a target requires one enantiomer, an ordinary achiral route may produce a racemate. Three broad planning strategies can introduce handedness: begin with a chiral-pool building…
Explore lesson ChemistryLessonChirality and Mirror Images
A left glove and a right glove are mirror images, but turning one in space never makes it fit the other hand. Some molecules have the same kind of handedness. Chirality matters…
Explore lesson ChemistryLabChirality and R/S
Assign R or S to a stereocentre and see what mirror images and SN2 reactions do to it.
Explore lesson ChemistryLessonChirality and Stereocentres
Hands have the same parts and mirror each other, yet a left hand cannot be placed exactly over a right hand with all fingers aligned. Some molecules show the same property. They…
Explore lesson ChemistryLessonChirality in Medicines and Biology
Two enantiomers have the same atom connections and many matching properties in an achiral environment. Living systems are not achiral: proteins, enzymes, sugars and nucleic acids…
Explore lesson ChemistryLessonChirality Without Stereocentres
A chiral molecule need not contain a tetrahedral carbon with four distinct groups. Chirality is defined by non-superimposability on a mirror image, so axes and stable twisted…
Explore lesson ChemistryLessonChlorine Formation from Brine
In a suitable concentrated-brine cell, chloride ions are oxidized at the positive anode to chlorine gas. The half-reaction is short but chemically important: two chloride ions…
Explore lesson ChemistryLessonChlorine in Water
Chlorine dissolved in water does more than remain as Cl₂ molecules. It undergoes hydrolysis to produce chloride and hypochlorous acid. The balance among Cl₂, HOCl and OCl⁻…
Explore lesson ChemistryLessonChoosing a Convenient Calculation Basis
Many composition problems give ratios rather than an actual sample amount. A convenient basis turns those ratios into simple numbers: 100 g of solution for mass percent, 1.00 L…
Explore lesson ChemistryLessonChoosing a Lewis Skeleton
Once the valence-electron budget is known, a Lewis structure needs a skeleton: which atoms connect to which? The formula often gives the numbers of atoms but does not fully…
Explore lesson ChemistryLessonChoosing a Metal for an Application
A material is useful because its properties fit a particular task. Copper conducts electricity very well, aluminium offers low density, steel offers varied structural strength…
Explore lesson ChemistryLessonChoosing a Separation Method
Because the substances in a mixture are not chemically bonded, they can be separated by physical methods. But which method? Filtering salt water gets you nowhere, and boiling…
Explore lesson ChemistryLessonChoosing an Analytical Method
There is no single best analytical technique for every chemical question. Titrimetry counts reaction equivalents through volume, gravimetry converts analyte to a weighed form…
Explore lesson ChemistryLessonChoosing an Electronic-Structure Method
There is no single electronic-structure method that is best for every molecule and property. Hartree–Fock, correlated wavefunction methods and density-functional approximations…
Explore lesson ChemistryLessonChoosing an Indicator for Titration
Universal indicator is excellent for estimating pH, so why is it almost never used in a titration? A titration depends on spotting the exact drop at which the acid is…
Explore lesson ChemistryLessonChoosing Approximation versus Exact Algebra
Physical chemistry is full of shortcuts: treating a weak acid as barely ionised, ignoring the hydrogen ions supplied by water, or assuming a gas is ideal. Each shortcut turns…
Explore lesson ChemistryLessonChoosing Equations for Ionic Equilibrium
Once you know how to write equilibrium expressions, mass balances and a charge balance, a practical question arises: which ones do you actually need? Write too few and the…
Explore lesson ChemistryLessonChoosing Metals for a Job
There is no single “best metal” for every object. A wire, a bridge component and a lightweight frame have different demands. Conductivity, strength, mass, shaping, corrosion…
Explore lesson ChemistryLessonChoosing Molecular Coordinates
A potential energy surface is independent of how we label a molecular geometry, but our calculations and explanations are not. Cartesian positions are universal and convenient…
Explore lesson ChemistryLessonChoosing Partners for Williamson Synthesis
An unsymmetric ether can often be drawn as two possible alkoxide–halide pairings. The better Williamson route puts the leaving group on the carbon most accessible to SN2 attack.…
Explore lesson ChemistryLessonChoosing SN1 or SN2
SN1 and SN2 are models for distinct substitution pathways, not labels chosen from a single clue. A primary substrate often supports SN2; a tertiary substrate can support SN1…
Explore lesson ChemistryLessonChoosing the Analytical Wavelength
A UV-visible spectrophotometer can be set to any wavelength across its range, yet an analyst measuring the concentration of a coloured solution almost always chooses one…
Explore lesson ChemistryLessonChoosing the Correct State Symbols
Choosing state symbols is an evidence task. A formula may represent a solid, a liquid, a gas or a dissolved substance depending on the situation. Begin with the question's…
Explore lesson ChemistryLessonChoosing the Longest Parent Chain
Selecting a parent chain is a graph problem, not a matter of drawing the longest horizontal line. A continuous chain can turn through a branch. For simple alkanes one chooses the…
Explore lesson ChemistryLessonChoosing the Parent Carbon Chain
Naming a branched carbon compound begins with choosing a parent structure. The longest visible line is a useful first guess, but an eligible parent must also contain the feature…
Explore lesson ChemistryLessonChoosing the Right Acid–Base Model
Acid–base questions can look similar while asking for different answers. “Which species donates a proton?” asks for a particle model. “How many moles react?” asks for…
Explore lesson ChemistryLessonChoosing the Right Material
Why are bridges made of steel and concrete rather than wood or glass? Why are drink bottles plastic or glass but not iron? Choosing a material means matching its properties to…
Explore lesson ChemistryLessonChromatography and Purity
In chemistry, a pure substance contains only one element or compound. Earlier in this unit, purity was tested with melting and boiling points. Chromatography offers a different…
Explore lesson ChemistryLabChromatography Learning Model
Explore the free chromatography chemistry station. Read the model assumptions, make a prediction and compare the numerical and visual results.
Explore lesson ChemistryLessonChromium and Copper Exceptions
Chromium and copper are standard reminders that an orbital filling mnemonic is an approximation. Their observed neutral ground-state occupancies differ from the simplest…
Explore lesson ChemistryLessonChromium and Manganese Chemistry
Chromium and manganese have several oxidation states and vivid oxoanion chemistry. Chromate and dichromate interconvert with pH while keeping Cr at +6. Permanganate contains Mn…
Explore lesson ChemistryLessonChromophores and Types of Transition
Only part of a molecule is usually responsible for its UV-visible absorption. In propanone, for example, the methyl groups contribute almost nothing, while the C=O group produces…
Explore lesson ChemistryLessonCIP Rules for Multiple Bonds and Isotopes
Simple CIP rankings use atomic number, but tied carbon branches often contain multiple bonds or isotopes. The formal duplicate-atom convention makes a double or triple bond…
Explore lesson ChemistryLessonCis-Trans Naming and Its Limits
Once geometric isomers are recognised, they need names. The oldest and most intuitive system uses the Latin words cis, "on this side", and trans, "across". For a simple alkene…
Explore lesson ChemistryLessonCis–Trans Photoisomerisation and Vision
A carbon–carbon double bond normally resists rotation because twisting disrupts π overlap. Light can excite a molecule and change the energetic cost of twisting, so cis and trans…
Explore lesson ChemistryLessonClaisen Condensation
An ester with an alpha hydrogen can form an enolate and attack a second ester molecule, creating a new C–C bond. Unlike an aldol addition to an aldehyde or ketone, the attacked…
Explore lesson ChemistryLessonClapeyron and Clausius–Clapeyron Revisited
The slope of a phase boundary is not just a feature to memorise from a diagram. It follows by differentiating equality of chemical potentials along the coexistence curve. The…
Explore lesson ChemistryLessonClassical Gas Partition Functions Revisited
The ideal-gas equation can be derived from molecular translation, but a postgraduate treatment must also get entropy and chemical potential right. The distinction between…
Explore lesson ChemistryLessonClassical Molecular Mechanics
Quantum calculations can describe bond rearrangement and electronic response, but they become expensive for a solvated protein, polymer or liquid containing many thousands of…
Explore lesson ChemistryLessonClassical Trajectory Simulations
A minimum-energy path describes where a molecule can travel on an energy landscape, but it does not say how a moving molecule actually travels. Classical trajectory simulations…
Explore lesson ChemistryLessonClassification and Periodicity: Unit Review
The periodic table links atomic identity to chemical prediction. Atomic number orders elements; electron configurations explain recurring group patterns; shielding and nuclear…
Explore lesson ChemistryCollectionClassification of Elements and Periodicity
Study Classification of Elements and Periodicity with 35 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonClassifying Anions for Analysis
Anions are often identified by a different logic from cations. Instead of one universal group-separation tree, an analyst chooses a small set of chemical reactions: some anions…
Explore lesson ChemistryLessonClassifying Carbon Atoms and Hydrogens
Organic mechanism descriptions often say primary, secondary or tertiary. For a carbon centre, these words count the number of other carbon atoms directly bonded to that centre.…
Explore lesson ChemistryLessonClassifying Cations into Analytical Groups
Classical cation analysis sorts ions into groups by which reagent causes them to precipitate under a specified sequence of conditions. The grouping is operational rather than a…
Explore lesson ChemistryLessonClassifying Isomers: A Stereochemical Map
A formula such as C₄H₈ does not uniquely specify a substance. But-1-ene, but-2-ene and cyclobutane differ in bonding, while two forms of but-2-ene differ only in spatial…
Explore lesson ChemistryLessonClassifying Ligands: L, X and Z Types
Electron counting becomes more reliable when ligands are classified by how they exchange electron pairs with a metal. The common L, X and Z scheme separates neutral donors…
Explore lesson ChemistryLessonClassifying Materials by Their Properties
There are millions of materials, but most fall into a handful of families with recognisable sets of properties. Sorting materials into groups lets chemists and engineers predict…
Explore lesson ChemistryLessonClassifying Pericyclic Reactions
Pericyclic chemistry includes several reaction families that look different on a structural drawing. Classifying the bond changes first makes the correct orbital rule easier to…
Explore lesson ChemistryLessonClassifying Phase Transitions
The word transition covers boiling, freezing, magnetic ordering and many other changes, but their thermodynamic signatures differ. At ordinary boiling, two phases coexist and a…
Explore lesson ChemistryLessonClassifying Polymers
There are thousands of commercial polymers, so chemists need ways to sort them. A single polymer can be described by where it comes from, by how it was made, by the shape of its…
Explore lesson ChemistryLessonClassifying Primary, Secondary and Tertiary Alcohols
Primary, secondary, and tertiary describe the carbon directly bonded to OH, not the number of OH groups in the molecule. This local carbon-neighbor count predicts whether a…
Explore lesson ChemistryLessonClassifying Primary, Secondary and Tertiary Amines
The words primary, secondary and tertiary have a precise meaning for amines: count the carbon-containing groups directly attached to nitrogen. A primary amine has one, a…
Explore lesson ChemistryLessonClassifying Solids
Solids resist flow because their constituent particles are held in relatively fixed arrangements, but not all solids have the same internal order or bonding. Crystal structures…
Explore lesson ChemistryLessonClassifying Unfamiliar Reactions
Real reactions do not promise to fit one classroom box. Burning magnesium is both combustion and combination; burning methane is combustion but produces two compounds.…
Explore lesson ChemistryLessonCleaner Fuels and Alternatives
Fossil fuels are convenient, energy-dense and cheap, but burning them adds carbon dioxide to the atmosphere and releases other pollutants. They are also finite. Chemists and…
Explore lesson ChemistryLessonClose-Packed Layers
Equal spheres can form a dense triangular layer, and the next layer nests in some of its hollows. Repeating this construction in two different ways produces cubic close packing…
Explore lesson ChemistryLessonCoagulation of Colloids
A stable-looking sol can become cloudy and separate after a small amount of electrolyte is added. This is coagulation: particles that previously remained apart now join into…
Explore lesson ChemistryLessonCoefficients as Reacting Ratios
Balanced coefficients do more than show that atoms match. They state the relative amounts of substances that react and form. A 2:1:2 equation can describe two molecules, two…
Explore lesson ChemistryLessonCoefficients Versus Subscripts
Compare 2H₂O with H₂O₂. Both contain the digits 2 and the symbols H and O, yet they describe entirely different things. The first means two molecules of water; the second means…
Explore lesson ChemistryLessonCoenzymes, Cofactors and Vitamins
Protein side chains can carry out many reactions, but cells also use non-protein helpers to extend the range of enzyme chemistry. Metal ions can polarise substrates or transfer…
Explore lesson ChemistryLessonCoffee-Cup Calorimetry
A foam-cup calorimeter is a simple way to measure heat from a reaction in solution. The vessel is close to atmospheric pressure, so the heat exchanged by the reaction can…
Explore lesson ChemistryLessonCollecting Gas over Water
A common laboratory collection method displaces water from an inverted container. The gas produced by a reaction occupies the container together with water vapour. Its measured…
Explore lesson ChemistryLessonColligative Effect from Solute Mass
A nonvolatile dissolved solute can lower a solvent's freezing point. A numerical problem often gives masses of solute and solvent rather than molality. The route is sequential…
Explore lesson ChemistryLabColligative properties
Dissolved particles lower the vapour pressure, raise the boiling point and lower the freezing point.
Explore lesson ChemistryLessonColligative Properties from Chemical Potential
Adding a nonvolatile solute can raise a solvent's boiling point and lower its freezing point. These two directions are consequences of one change: mixing lowers the liquid…
Explore lesson ChemistryLessonColligative Properties: Counting Particles
Some solution properties depend mainly on how many effective solute particles are dissolved rather than the specific chemical identity of each particle. These are called…
Explore lesson ChemistryLessonCollision Energy and Scattering
Reaction rates average over enormous numbers of molecular encounters. Scattering studies focus on what happens in an individual class of encounters with specified collision…
Explore lesson ChemistryLessonCollision Frequency and Collision Cross-Section
Kinetic theory says gas molecules collide, but a reaction-rate estimate needs to count how often. A hard-sphere model treats molecules as spheres with fixed radii and asks when…
Explore lesson ChemistryLabCollision theory
A + B molecules collide. Only collisions with enough energy and the right orientation react.
Explore lesson ChemistryLessonCollision Theory
Molecules must interact before they can exchange atoms or electrons, but most encounters do not necessarily make product. Collision theory explains rates using encounter…
Explore lesson ChemistryLessonColloidal Dispersions
Milk, fog and many paints look uniform from a distance but contain distinct phases on a smaller scale. They are colloidal dispersions. Their behavior depends on which phase is…
Explore lesson ChemistryLessonColloidal Nanoparticle Synthesis
Colloidal synthesis builds nanoparticles in a liquid where molecular precursors react, tiny nuclei appear and those nuclei grow while surrounded by ligands and solvent. The…
Explore lesson ChemistryLessonColloidal Stability and Aggregation
A stable nanoparticle core is not necessarily a stable nanoparticle dispersion. Particles in a liquid collide constantly and may stick together, changing their hydrodynamic size…
Explore lesson ChemistryLabColloids
Colloids: light scattering (Tyndall effect), coagulation by salts, and soap micelles.
Explore lesson ChemistryLessonColour and Complementary Colours
A solution of copper(II) sulfate looks blue, yet copper(II) ions do not emit blue light. Instead, they absorb light at the red–orange end of the spectrum, and the remaining light…
Explore lesson ChemistryLessonColour Centres in Crystals
Pure alkali-halide crystals are commonly transparent in the visible region, yet irradiating or chemically reducing one can make it coloured. The change need not mean a new bulk…
Explore lesson ChemistryLessonColour Change as Evidence
A cut apple turns brown, a copper roof slowly turns green, and red cabbage juice turns pink in vinegar. Colour changes are among the easiest signs of change to spot, and they…
Explore lesson ChemistryLessonColour of Coordination Compounds
Coordination compounds can be vividly coloured because their electronic states absorb portions of visible light. The colour we see is usually the light transmitted or reflected…
Explore lesson ChemistryLessonColour, Lustre and Transparency
The first things we notice about a material are usually how it looks: its colour, whether it shines and whether we can see through it. These visual properties arise from how the…
Explore lesson ChemistryLessonColumn Chromatography
Column chromatography turns the migration idea of TLC into a flow-through separation. A sample enters a column containing a stationary bed, and mobile fluid carries components…
Explore lesson ChemistryLessonCombination and Decomposition as Opposites
A combination equation can often be written backward as a decomposition equation, and vice versa. CaO + CO₂ → CaCO₃ joins two substances into one; CaCO₃ → CaO + CO₂ splits one…
Explore lesson ChemistryLessonCombination and Decomposition Redox
“Combination” and “decomposition” describe how many reactant and product formulas appear in an equation. “Redox” describes whether oxidation numbers change. These labels answer…
Explore lesson ChemistryLessonCombination Reactions in Industry and Daily Life
Reaction categories become more useful when linked to real settings. Ammonia synthesis supplies a major chemical feedstock, slaking lime makes calcium hydroxide for practical…
Explore lesson ChemistryLessonCombination Reactions: The Basic Idea
In a combination reaction, two or more reactant substances form one product substance. The equation may involve elements, compounds or both. Counting distinct substances reveals…
Explore lesson ChemistryLessonCombined Gas Law
Boyle's, Charles's and the pressure-temperature laws each hold one variable fixed. A gas sample may instead change pressure, volume and temperature together. If its amount…
Explore lesson ChemistryLessonCombining Advanced Spectroscopies
No single spectroscopy tells the whole story of a molecule or material. NMR maps connectivity and dynamics in diamagnetic molecules, EPR sees only unpaired electrons, Mössbauer…
Explore lesson ChemistryLessonCombining Equilibrium Reactions
Some desired equilibrium reactions are sums of simpler reactions whose constants are known. When equations are added, their thermodynamic constants multiply. Intermediates that…
Explore lesson ChemistryLessonCombining Half-Reactions
Balancing each half-reaction is only part of the job. A final chemical equation must have exactly as many electrons released by oxidation as consumed by reduction, so no…
Explore lesson ChemistryLessonCombining IR and Mass Spectrometry
Infrared spectroscopy tells you what kind of compound you have — an alcohol, a ketone, a carboxylic acid — but says little about its size. Mass spectrometry tells you how heavy…
Explore lesson ChemistryLessonCombining Mechanistic and Data-Driven Models
Mechanistic models encode what is known about atoms, sites and rates; data-driven models can capture patterns where parameters are uncertain or exhaustive calculation is costly.…
Explore lesson ChemistryLessonCombining NMR with Other Techniques
Mass spectrometry and IR tell you how big a molecule is and which functional groups it carries, but they rarely show how the atoms are joined. Nuclear magnetic resonance fills…
Explore lesson ChemistryLessonCombining Simple Half-Reactions
Two correct half-reactions may not yet fit together. One might release three electrons for each atom while the other accepts two. Multiply whole half-reactions so the released…
Explore lesson ChemistryLessonCombining Structural and Stereoisomer Counts
A formula can support more than cis/trans or optical isomers. A ligand may swap with a counterion, or an ambidentate ligand may attach through different atoms. These are…
Explore lesson ChemistryLessonCombining Symmetry Operations
Recognising individual symmetry elements is only the beginning. Applying one valid operation and then another also leaves a molecule indistinguishable from its start. The…
Explore lesson ChemistryLessonCombining Thermochemical Equations
With three or more supplied equations, Hess's law becomes a careful bookkeeping problem. Each supplied reaction can be reversed or multiplied, but the final sum must reproduce…
Explore lesson ChemistryLessonCombining Volumes of Reacting Gases
Reacting gases often show simple whole-number volume ratios when all gas volumes are compared at the same temperature and pressure. Two volumes hydrogen can react with one volume…
Explore lesson ChemistryLessonCombustion Across Organic Families
Alkanes, alkenes, alcohols and many other organic compounds can burn. For complete combustion of a compound containing C, H and O, the carbon atoms become CO₂ and hydrogen atoms…
Explore lesson ChemistryLessonCombustion Analysis
Burning an organic sample completely can turn its carbon into CO₂ and its hydrogen into H₂O. Measuring those products reveals how much carbon and hydrogen the original sample…
Explore lesson ChemistryLessonCombustion Analysis of Carbon and Hydrogen
When a carbon- and hydrogen-containing sample burns completely in excess oxygen, its carbon is represented in collected CO₂ and its hydrogen in collected H₂O. Product masses can…
Explore lesson ChemistryLessonCombustion Analysis with Oxygen Difference
Burning an organic sample completely can convert its carbon into CO₂ and hydrogen into H₂O. Measured product masses then reveal how much C and H were in the original sample. If…
Explore lesson ChemistryLessonCombustion and Chain-Branching Networks
Combustion is not one balanced arrow from fuel and oxygen to carbon dioxide and water. It is a large network of radical reactions with changing temperature. Chain carriers can…
Explore lesson ChemistryLessonCombustion and the Carbon Cycle
Every carbon atom in your body has been somewhere else before: in the air, in a plant, perhaps in an ancient ocean or a lump of coal. Carbon is constantly recycled between living…
Explore lesson ChemistryLessonCombustion and the Environment
Burning fuels heats our homes, powers most of our transport and generates much of our electricity. But the products of combustion do not simply disappear: they enter the…
Explore lesson ChemistryLessonCombustion as an Exothermic Reaction
We burn fuels for one reason: to get energy out of them. A gas hob heats a pan, a car engine turns wheels and a power station makes electricity, all by combustion. But where does…
Explore lesson ChemistryLessonCommittor Analysis
A coordinate can produce a smooth free-energy barrier and still be poor at predicting reaction. Two configurations with the same bond distance may have different solvent…
Explore lesson ChemistryLessonCommon 2D NMR Artefacts
A 2D NMR contour map seems pictorially definite: one spot appears to connect two resonances. Yet a spot can be a true transfer, an expected diagonal signal, a second molecule at…
Explore lesson ChemistryLessonCommon Acids and Their Formulae
Chemistry laboratories use dozens of acids, but four turn up again and again: hydrochloric acid, sulfuric acid, nitric acid and ethanoic acid. Knowing their formulae is like…
Explore lesson ChemistryLessonCommon Bases and Their Formulae
If acids are defined by the hydrogen ions they release, bases are defined by what they do to those ions: they neutralise them. Bases come in several families — metal oxides…
Explore lesson ChemistryLessonCommon Coordination Geometries
Coordination number tells how many donor atoms surround a metal, while geometry tells where those donors sit in three-dimensional space. Common patterns are linear for two…
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