THE LESSON LIBRARY / CHEMISTRY
Chemistry, explored.
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Electrolysis of Water
Water can be split into hydrogen and oxygen by an appropriately designed electrolytic cell supplied with electrical energy. Pure water conducts poorly, so practical cells use a…
Explore lesson ChemistryLessonElectrolyte Conductivity
An electrolyte carries electrical current through ion motion in solution. A meter first observes resistance or conductance of a particular cell; conductivity removes the cell's…
Explore lesson ChemistryLessonElectrolytes and Ionic Equilibrium
Some dissolved substances create many mobile ions, while others remain largely in a molecular form. This difference determines how their aqueous mixtures conduct electricity and…
Explore lesson ChemistryLessonElectrolytes and Nonelectrolytes
Two colorless solutions can behave very differently in an electrical circuit. Sodium chloride solution conducts because mobile ions carry charge. A sugar solution of similar…
Explore lesson ChemistryLessonElectrolytes and the Solid–Electrolyte Interphase
The electrolyte must carry lithium ions between electrodes while remaining electronically insulating and sufficiently stable at both electrode potentials. In many graphite-based…
Explore lesson ChemistryLessonElectrolytic Cells
An electrolytic cell uses an external power source to drive a redox reaction that is not spontaneous in its intended direction under the operating conditions. Its electrodes…
Explore lesson ChemistryLessonElectrolytic Decomposition of Water
Electricity can drive water to decompose into hydrogen and oxygen gases. The balanced equation 2H₂O(l) → 2H₂(g) + O₂(g) shows one reactant substance giving two products and…
Explore lesson ChemistryLessonElectrolytic Extraction of Reactive Metals
Some metals form oxides or salts so stable that ordinary carbon reduction is unsuitable. An external power supply can force electrons into their cations and produce the metal.…
Explore lesson ChemistryLessonElectrolytic Refining of Copper
Crude copper can contain impurities that interfere with demanding uses. Electrolytic refining transfers copper from an impure anode through an electrolyte onto a cathode as…
Explore lesson ChemistryLessonElectromagnetic Radiation
Atomic spectra are measured as light wavelengths or frequencies, while atomic transitions are described as energy changes. Electromagnetic-radiation equations connect these…
Explore lesson ChemistryLessonElectron Affinity and Electron Gain
Ionisation asks what happens when an electron is removed; electron affinity asks about adding one. A chlorine atom in the gas phase can accept an electron to form Cl⁻, and the…
Explore lesson ChemistryLessonElectron Arrangement and Ion Formation
Why does sodium commonly appear as Na⁺ and chlorine as Cl⁻ in sodium chloride? Their neutral electron arrangements provide a useful first explanation: sodium can lose its single…
Explore lesson ChemistryLessonElectron Arrangement and Periodic Table Position
The periodic table's rows and columns encode useful information about electronic structure. For early main-group atoms, a shell arrangement can lead directly to period and group.…
Explore lesson ChemistryLessonElectron Arrangements of Ions
Common ions can often be understood by comparing their electron arrangement with that of the neutral parent atom. Metals in early main groups commonly lose outer electrons, while…
Explore lesson ChemistryLessonElectron Arrangements of the First Twenty Elements
Once you know that electrons fill shells in order, you can write down the electron arrangement of an atom in a few seconds. A short code such as 2,8,1 tells you how many…
Explore lesson ChemistryLessonElectron Balance as a Reaction Check
A proposed redox equation should conserve atoms, total charge and electron equivalents. Oxidation-number increases and decreases, weighted by coefficients, must match in a…
Explore lesson ChemistryLessonElectron Capacity of a Shell
The expression 2n² gives the maximum number of electrons that can occupy all orbitals belonging to a shell with principal number n. It yields 2 for n = 1, 8 for n = 2 and 18 for…
Explore lesson ChemistryLessonElectron Capture
Electron capture is a way for some proton-rich nuclides to reduce their proton count without emitting a positron. A proton in the nucleus combines with an atomic electron…
Explore lesson ChemistryLessonElectron Carriers: NAD, NADP and FAD
Oxidising a nutrient is useful only if its electrons can be captured and delivered to another reaction. NAD, NADP and FAD are coenzymes that perform this transfer with different…
Explore lesson ChemistryLessonElectron Charge and Mass
Thomson found that cathode-ray particles have a very large charge-to-mass ratio. That result alone could not tell whether their charge was unusually large, their mass unusually…
Explore lesson ChemistryLessonElectron Configuration and Periodic Position
An electron configuration links the periodic table to atomic structure. It records where an atom's electrons occupy orbitals in its ground state. From it, one can usually find a…
Explore lesson ChemistryLessonElectron Configurations Across Period Three
Period three repeats a familiar outer-electron pattern at a larger principal number. Sodium and magnesium fill 3s after the neon core; aluminium through argon add electrons to…
Explore lesson ChemistryLessonElectron Configurations Across Period Two
Period two offers a compact tour of Aufbau, Pauli and Hund rules. Lithium starts adding electrons beyond the helium core into 2s; after 2s fills, boron through neon fill the…
Explore lesson ChemistryLessonElectron Configurations of Anions
An anion forms when an atom gains electrons while keeping its proton number fixed. Common nonmetals gain enough electrons to fill an outer p subshell in elementary configuration…
Explore lesson ChemistryLessonElectron Configurations of Cations
Forming a cation removes electrons while leaving the nucleus and atomic number unchanged. The first task is counting how many electrons remain. The second is choosing which…
Explore lesson ChemistryLessonElectron Configurations of Transition Metal Ions
Every crystal-field diagram starts with a d-electron count. A wrong count makes the subsequent spin state, stabilisation energy and magnetic moment wrong even if the diagram is…
Explore lesson ChemistryLessonElectron Correlation Beyond Hartree–Fock
Hartree–Fock optimises one antisymmetric determinant and includes average Coulomb repulsion and exchange. It does not fully describe how electrons adjust their positions in…
Explore lesson ChemistryLessonElectron Counting by Two Methods
Valence electron counting is a bookkeeping tool for organometallic structures. The ionic and covalent methods assign electrons differently to metal–ligand bonds but must produce…
Explore lesson ChemistryLessonElectron Diffraction
The matter-wave proposal became convincing when electrons produced diffraction patterns. A crystal's regularly spaced atoms provide a fine-scale structure suitable for…
Explore lesson ChemistryLessonElectron Flow and Ion Migration
An electrolysis diagram often contains arrows for electrons and ions. They must not be treated as the same particles crossing every region. Electrons travel through the external…
Explore lesson ChemistryLessonElectron Gain Defines Reduction
Reduction is electron gain in the simple electron-transfer description. A positive metal ion can accept electrons and become a less positively charged ion or a neutral metal…
Explore lesson ChemistryLessonElectron Gain Enthalpy
Electron gain enthalpy describes the energy change when an electron is added to an isolated gaseous atom. It is useful for interpreting how readily certain atoms form monatomic…
Explore lesson ChemistryLessonElectron Gain Trends and Exceptions
Electron gain enthalpy has useful periodic patterns, but they are less regular than a single arrow suggests. Halogens often release substantial energy when they gain an electron…
Explore lesson ChemistryLessonElectron Loss Defines Oxidation
The general electron definition of oxidation is loss of electrons. It covers reactions with no oxygen, including metals entering solution as positive ions. A written…
Explore lesson ChemistryLessonElectron Paramagnetic Resonance: Principles
Electron paramagnetic resonance, also called electron spin resonance, detects species with unpaired electrons. Organic radicals, many transition-metal ions and certain defects in…
Explore lesson ChemistryLessonElectron Sharing: The Covalent Bond
Non-metal atoms often join without forming the separate positive and negative ions used in a simple salt model. Instead, electrons are shared between them. Covalent bonding…
Explore lesson ChemistryLessonElectron Shells and the Periodic Table
The periodic table was first built by comparing how elements behave, long before anyone knew what was inside an atom. When scientists discovered that electrons are arranged in…
Explore lesson ChemistryLessonElectron Shielding Across the Table
Potassium's nucleus has more protons than sodium's, yet its outer electron is generally easier to remove. The electron sits farther out and encounters more inner-electron…
Explore lesson ChemistryLessonElectron Spin and the Spin Quantum Number
The Schrödinger equation for hydrogen produces three quantum numbers, n, l and mₗ, all arising from motion in three-dimensional space. Yet atomic spectra and the structure of the…
Explore lesson ChemistryLessonElectron Spin Quantum Number
Three quantum numbers identify an orbital's spatial state, but an electron has another quantum label: spin projection. Its two allowed values provide the final distinction…
Explore lesson ChemistryLessonElectron Transfer and Marcus Theory
An electron can move from a donor to an acceptor without a conventional bond-breaking event. Why, then, is electron transfer not always instantaneous? The surrounding nuclei and…
Explore lesson ChemistryLessonElectron Transfer and Oxidation Numbers
Redox reactions involve coupled oxidation and reduction. In a simple reaction between a metal and metal ion, actual electron transfer can be written explicitly. In a covalent…
Explore lesson ChemistryLessonElectron Transfer in Metal Displacement
Metal displacement gives a concrete electron-transfer example. A metal atom can enter solution as an ion while ions of a different metal become atoms in a deposit. The two…
Explore lesson ChemistryLessonElectron Transfer: How Ions Form
A neutral atom has equal numbers of protons and electrons. Transfer an electron and that balance changes, creating an ion without changing the element's nucleus. Following the…
Explore lesson ChemistryLessonElectron-Affinity Trends with Caution
It is tempting to draw one arrow showing electron affinity becoming “stronger” toward the upper right of the table. That arrow hides important exceptions. Adding to a filled s…
Explore lesson ChemistryLessonElectron-Deficient Compounds
Not every stable molecule satisfies the simple octet rule in a localized Lewis picture. BF₃ has only six electrons around boron in its straightforward three-bond structure, while…
Explore lesson ChemistryLessonElectron-Deficient Lewis Structures
The octet rule is a good first check for many second-period atoms, but it does not make every six-electron center a mistake. Boron trifluoride, BF₃, is a familiar example: the…
Explore lesson ChemistryLessonElectron-Domain Repulsion Model
Lewis structures tell us which atoms connect and where lone pairs are represented, but a flat page does not specify three-dimensional positions. VSEPR uses regions of valence…
Explore lesson ChemistryLessonElectron-Withdrawing and Donating Inductive Groups
Inductive labels compress a comparison: a substituent may draw electron density through sigma bonds or push it relative to another group. The labels +I and −I are useful only…
Explore lesson ChemistryLessonElectron–Hole Generation and Separation
Photon absorption is the first step in photovoltaic conversion, not the last. An absorbed photon can promote an electron to a higher-energy state and leave a hole behind. Those…
Explore lesson ChemistryLessonElectronegativity Across a Period
Across a main-group period, neutral atoms generally attract bonding electrons more strongly toward the right. Rising proton number with broadly similar core shielding helps…
Explore lesson ChemistryLessonElectronegativity and Chemical Shift
Shielding explains why signals move, but a chemist interpreting a spectrum needs to predict how far. The single most useful guide for protons on saturated carbon atoms is the…
Explore lesson ChemistryLessonElectronegativity and Polar Bonds
A Lewis line tells us that a bonding electron pair is represented between atoms, but not how that density is shared. Electronegativity gives a qualitative guide: an atom with…
Explore lesson ChemistryLessonElectronegativity Down a Group
Fluorine, chlorine, bromine and iodine are related halogens, but their ability to pull shared bonding electrons is not identical. Down the group, outer electrons occupy higher…
Explore lesson ChemistryLessonElectronegativity in a Bond
In an H–Cl bond, the shared electrons spend more density toward chlorine than hydrogen. Electronegativity describes this relative attraction in a bonding context. It helps…
Explore lesson ChemistryLessonElectronegativity in Bonds
Electronegativity describes how strongly an atom attracts shared electrons when it is bonded to another atom. It helps explain why H–Cl has unequal electron density and why many…
Explore lesson ChemistryLessonElectronegativity Trends
Electronegativity generally increases across a main-group period and decreases down a group. Fluorine is the highest element on the familiar Pauling scale. These arrows are…
Explore lesson ChemistryLessonElectronegativity: Unequal Sharing
The phrase shared electrons does not promise equal sharing. Two different atoms may attract the bonding electron density with different strengths. Electronegativity describes…
Explore lesson ChemistryLessonElectronic and Magnetic Contributions to Heat Capacity
Heat capacity can reveal energy levels beyond molecular vibration and crystal phonons. A magnetic field may split spin states; an atom or ion may have a low-lying electronic…
Explore lesson ChemistryLabElectronic effects
Electron-pushing and electron-pulling groups change acidity and where reactions happen.
Explore lesson ChemistryLessonElectronic Excited States
Light absorption changes a molecule's electronic state much faster than heavy nuclei usually change position. The initially excited molecule therefore retains approximately its…
Explore lesson ChemistryLessonElectronic Transition Selection Rules
An electronic excited state may be energetically accessible yet produce little or no absorption under ordinary light. Energy conservation determines where a transition could…
Explore lesson ChemistryLessonElectronic Transitions and UV-Visible Absorption
Infrared radiation makes bonds vibrate, but it does not carry enough energy to disturb the electrons that hold a molecule together. Move to shorter wavelengths, into the…
Explore lesson ChemistryLessonElectronic, Enthalpic and Free-Energy Barriers
One energy diagram can carry several different vertical scales. A computed electronic barrier, a thermally corrected enthalpy barrier and a standard Gibbs free-energy barrier…
Explore lesson ChemistryLessonElectrophiles and Nucleophiles — Organic Chemistry: Basic Principles
Many organic mechanisms begin with one species providing an electron pair and another accepting it. The donor is called a nucleophile; the acceptor is an electrophile. These are…
Explore lesson ChemistryLessonElectrophiles and Nucleophiles — Organic Mechanisms and Named Reactions
Many polar organic mechanisms begin when an electron-rich site meets an electron-poor site. The donor is a nucleophile, and the acceptor is an electrophile. These roles depend on…
Explore lesson ChemistryLabElectrophilic addition to alkene
Electrophilic addition of HBr to an alkene, through a carbocation (Markovnikov’s rule).
Explore lesson ChemistryLessonElectrophilic Addition to Alkenes
The alkene π electron cloud is exposed above and below its sigma framework and can interact with an electron-pair acceptor. In electrophilic addition, the π component is consumed…
Explore lesson ChemistryLabElectrophilic aromatic substitution
Electrophilic substitution of benzene: an arenium ion forms, then loses H⁺ to become aromatic again.
Explore lesson ChemistryLessonElectrophilic Aromatic Substitution
Electrophilic aromatic substitution replaces a hydrogen on an aromatic ring with an electrophilic group. The reaction temporarily sacrifices aromaticity when the electrophile…
Explore lesson ChemistryLessonElectrophilic Aromatic Substitution Overview
The pi electrons of benzene can react with electrophiles, but benzene behaves differently from an ordinary alkene. Instead of simply adding two groups across one double bond and…
Explore lesson ChemistryLessonElectrophilic Substitution of Phenol
Phenol reacts at its aromatic ring more readily than benzene in many electrophilic substitution reactions. The hydroxyl oxygen can donate electron density into the ring by…
Explore lesson ChemistryLessonElectroplating
Chromium on bathroom taps, gold on electrical connectors and copper filling the microscopic wiring channels in computer chips are all electroplated. Electroplating uses an…
Explore lesson ChemistryLessonElectroplating and Industrial Electrolysis
Electrolysis is useful when a nonspontaneous reaction produces a valuable material or surface. Electroplating deposits a metal film onto a conducting object. Industrial…
Explore lesson ChemistryLessonElectroplating Basics
Electroplating deposits a metal layer on an object using an external electrical supply. The object to be coated acts as a cathode, where dissolved metal ions gain electrons and…
Explore lesson ChemistryLessonElectroplating Fundamentals
Electroplating places a thin metal layer on a conducting object using an electrical power supply. The object is connected as the cathode, where dissolved metal ions gain…
Explore lesson ChemistryLabElectroplating Learning Model
Explore the free electroplating chemistry station. Read the model assumptions, make a prediction and compare the numerical and visual results.
Explore lesson ChemistryLessonElectrosynthesis
In conventional synthesis, an oxidation or reduction needs a chemical reagent, often used in stoichiometric amounts and producing waste. In electrosynthesis, electrons themselves…
Explore lesson ChemistryLessonElement Plus Element Combinations
When two elements combine, the product often contains both elements, but the formula cannot be found by simply joining their symbols. Ionic charges, covalent bonding and the…
Explore lesson ChemistryLabElemental analysis
Work out percentage composition and the empirical formula from combustion and nitrogen analysis.
Explore lesson ChemistryLessonElementary Steps and Mechanisms
A net chemical equation reports reactants and products, but it can conceal a sequence of molecular events. A mechanism proposes those elementary steps. Any acceptable proposal…
Explore lesson ChemistryLessonElementary-Step Rate Laws
A reaction network's arrows become a kinetic model when each arrow is assigned a flux law. For a genuine elementary collision or transformation, mass-action kinetics relates that…
Explore lesson ChemistryLessonElements and Compounds in Everyday Life
Chemistry is not confined to the laboratory. Every breath you take, every meal you eat and every object you touch is made of elements and compounds. The air contains nitrogen and…
Explore lesson ChemistryLessonElements at Room Temperature
Look around you and almost every element you can name is a solid: the iron in a railing, the copper in a cable, the carbon in pencil lead. Yet the air you breathe is mostly two…
Explore lesson ChemistryLessonElements Beyond Uranium
For most of history, the heaviest element known was uranium, with atomic number 92. Today the periodic table has 118 elements, and every one after uranium was first made by…
Explore lesson ChemistryLessonElements Named After Places, People and Properties
Every element name tells a story. Some honour the country where an element was discovered, some celebrate famous scientists, and others describe a colour, a smell or a behaviour.…
Explore lesson ChemistryLessonElements of Period 3
A single row of the periodic table can show almost every kind of element in chemistry. Period 3 begins with sodium, a soft and highly reactive metal, and ends with argon, an…
Explore lesson ChemistryLessonElements That Exist as Molecules
When we say that the air contains oxygen, we do not mean that it contains loose oxygen atoms floating on their own. Almost all the oxygen in air is made of pairs of oxygen atoms…
Explore lesson ChemistryLessonElements, Compounds and Mixtures
There are millions of different materials, yet chemists sort all matter into just three families: elements, compounds and mixtures. Knowing which family a material belongs to…
Explore lesson ChemistryCollectionElements, Compounds and Symbols
Study Elements, Compounds and Symbols with 50 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonElements, Compounds and Symbols: Unit Review
This unit has taken you from the simplest substances — elements — to the language chemists use to describe everything built from them. You have learned element symbols, how…
Explore lesson ChemistryLessonElements: The Simplest Substances
Everything around you — the air, your desk, the water in your bottle, your own body — is built from a surprisingly short list of basic ingredients. Chemists call these…
Explore lesson ChemistryLessonElimination from Haloalkanes
A haloalkane can lose a halogen and a hydrogen from neighboring carbons to form an alkene. This is elimination rather than substitution: no new nucleophile bond replaces C–X, and…
Explore lesson ChemistryLessonEllingham Diagrams
To decide whether carbon, CO or another metal can remove oxygen from an oxide, compare the free energies of competing oxidation reactions. An Ellingham diagram places standard…
Explore lesson ChemistryLessonEmerging Battery Chemistries
No battery chemistry is best for every use. Materials cost, mass, lifetime, power, safety and scalability pull designs in different directions. Sodium-ion, solid-state…
Explore lesson ChemistryLessonEmission and Relaxation
An excited atom can release light as it settles to a lower energy state. In an energy-level diagram the arrow points downward, while the emitted photon carries the positive…
Explore lesson ChemistryLessonEmpirical Formula from Composition Data
Elemental composition is usually measured by mass, but chemical formulas count atoms. The bridge is the mole: convert each element's mass to moles, divide by the smallest amount…
Explore lesson ChemistryLessonEmpirical Formula from Element Masses
Element masses do not directly reveal atom counts: a gram of hydrogen contains many more atoms than a gram of oxygen. To infer a compound's simplest formula, convert each element…
Explore lesson ChemistryLessonEmpirical Formula from Percentages
Elemental analysis often reports percentages rather than individual gram masses. Choosing an imagined 100 g pure sample turns each mass percentage into the same numerical number…
Explore lesson ChemistryLessonEmpirical Formulas from Composition
Experimental analysis usually reports masses or mass percentages, whereas a formula reports ratios of atoms. The bridge is amount in moles. Dividing masses directly can fail…
Explore lesson ChemistryLessonEmpirical Formulas of Hydrates
Some ionic solids include water as part of a definite crystal composition. A hydrate formula such as CuSO₄·5H₂O states five water units per CuSO₄ formula unit. Heating data can…
Explore lesson ChemistryLessonEmulsions and Emulsifiers
Oil and water usually separate after shaking, yet milk and mayonnaise can remain dispersed for useful periods. Their persistence depends on more than vigorous mixing: new…
Explore lesson ChemistryLessonEnamine Formation
Primary amines and carbonyl compounds commonly give imines. Secondary amines initially follow a similar path but usually finish differently: after water leaves, the iminium…
Explore lesson ChemistryLessonEnamines as Enolate Equivalents
An enamine is a neutral C=C–NR2 compound made from a carbonyl compound and a secondary amine. Its alkene carbon adjacent to nitrogen is nucleophilic, so it can form a new bond at…
Explore lesson ChemistryLessonEnantiomeric Excess
A sample described as “mostly R” needs a number. Enantiomeric excess, ee, measures the imbalance between the two enantiomers. It is zero for a racemate and 100% for a pure single…
Explore lesson ChemistryLessonEnantiomers and Optical Activity
Two enantiomers have the same bond connections and nearly identical properties in an achiral setting, yet one can rotate plane-polarised light clockwise and the other equally in…
Explore lesson ChemistryLessonEnantiomers and Their Properties
Enantiomers are the left- and right-handed forms of a chiral structure. They share formula and connectivity but cannot be superimposed. Their similarity in an achiral laboratory…
Explore lesson ChemistryLessonEnergy and the Water Cycle
The water cycle never stops: every second, enormous amounts of water evaporate from the oceans, drift through the air as vapour, condense into clouds and fall back as rain.…
Explore lesson ChemistryLessonEnergy Barriers in a Reaction Network
Computer calculations can supply energies for reactants, intermediates and transition states, but a network needs rates. Converting an energy diagram into a kinetic model…
Explore lesson ChemistryLessonEnergy Changes in Combination Reactions
Many familiar combinations release heat: magnesium burning in oxygen, hydrogen reacting with oxygen, and quicklime reacting with water. It is tempting to say that joining…
Explore lesson ChemistryLessonEnergy Changes in Neutralisation
If you mix dilute hydrochloric acid with dilute sodium hydroxide solution in an insulated cup, the thermometer climbs by several degrees within seconds. Nothing fizzes and…
Explore lesson ChemistryLessonEnergy Changes: Heat and Light
A lit match flares with a bright yellow flame. A hand warmer grows hot in your pocket. A cold pack goes icy when you squeeze it. Each of these is a chemical change, and in each…
Explore lesson ChemistryLessonEnergy Demand of Electrolysis
Electrolysis uses electricity as a major process input, so a product amount alone is not enough to judge performance. Current determines how much charge passes, voltage…
Explore lesson ChemistryLessonEnergy Demands of Metal Extraction
Metal extraction rearranges stable compounds and separates products, so it needs energy as well as reactants. A blast furnace uses heat and reducing gas; an electrolytic smelter…
Explore lesson ChemistryLessonEnergy Equipartition and Its Boundaries
Classical statistical mechanics offers a powerful shortcut: each independent quadratic energy term contributes kT/2 to mean thermal energy. It explains gas translation and…
Explore lesson ChemistryLessonEnergy Integration: Heat Exchangers
An industrial reactor may release hot product while its incoming feed needs heating. Cooling the product with water and heating the feed separately with fuel wastes an…
Explore lesson ChemistryLessonEnergy Levels and Shells
The rings in a shell diagram and the lines in an energy diagram are easy to confuse. Rings organise a simplified picture of electron states around the nucleus; horizontal lines…
Explore lesson ChemistryLessonEnergy Levels of the Hydrogen Atom
Solving the radial equation for hydrogen yields one of the most celebrated results in science: the energy levels depend on a single integer and fall as 1/n². The formula…
Explore lesson ChemistryLessonEnergy Levels of the Particle in a Box
The boundary conditions of the one-dimensional box allow only waves with k = nπ/L. Turning that result into a formula for the energy gives one of the most widely used equations…
Explore lesson ChemistryCollectionEnergy Materials: Batteries and Photovoltaics
Study Energy Materials: Batteries and Photovoltaics with 40 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonEnergy Materials: Matching Function to Structure
A material cannot be judged for an energy device by one attractive number. A battery electrode may store many ions but fail if those ions cannot move quickly or if repeated…
Explore lesson ChemistryLessonEnergy Materials: Unit Review
The central idea of energy-materials chemistry is a chain of consequences. Composition and processing determine crystal structure, defects, particle or film morphology and…
Explore lesson ChemistryLessonEnergy Transfer and Master Equations
An energy-resolved RRKM rate k(E) tells how rapidly a molecule reacts if its internal energy is E. A gas-phase sample contains molecules at many energies, and collisions with a…
Explore lesson ChemistryLessonEnergy Transfer Between Molecules
One molecule can absorb light while a nearby molecule becomes excited. This energy transfer does not necessarily move a net electron or form a chemical product. Two important…
Explore lesson ChemistryLessonEnergy Transfer During Changes of State
An ice cube melting in your hand makes your skin feel cold. A burn from steam can be worse than a burn from boiling water. A farmer may spray orange trees with water on a frosty…
Explore lesson ChemistryLessonEnolate Chemistry in Living Systems
Enolates are not restricted to flasks containing LDA. Living systems form and stabilise enolate-like or enamine intermediates in enzyme active sites, using carefully placed…
Explore lesson ChemistryLessonEnolate Chemistry: Checkpoint Review
The carbon next to a carbonyl can become nucleophilic after an alpha hydrogen is removed. That single idea connects enol formation, enolate alkylation, aldol addition, Claisen…
Explore lesson ChemistryLessonEnolate Ions as Nucleophiles
In the previous topic we saw that a base can remove an α-hydrogen from an aldehyde or ketone to give an enolate ion. That anion is more than a stepping stone to the enol. It is a…
Explore lesson ChemistryLessonEnols and Enolates
A carbonyl compound with a hydrogen on a neighbouring carbon has reactivity beyond simple attack at C=O. A base can remove that alpha hydrogen, creating an enolate whose negative…
Explore lesson ChemistryLessonEnthalpy and Entropy of Activation
An energy diagram often labels a single barrier height, but a reaction rate responds to a free-energy bottleneck. Reaching the transition state can require both an enthalpy cost…
Explore lesson ChemistryLessonEnthalpy as U + PV
Many laboratory reactions occur near constant atmospheric pressure. When gases expand or contract, pressure-volume work affects the heat observed. Enthalpy, defined by H = U +…
Explore lesson ChemistryLessonEnthalpy of Atomisation
Many thermochemical cycles need gaseous atoms as intermediates. Atomisation enthalpy measures the energy required to produce them from an element's reference state. For a metal…
Explore lesson ChemistryLessonEnthalpy of Combustion
Combustion enthalpy quantifies heat release when a fuel reacts completely with oxygen under specified conditions. For a standard molar value, the equation is normally scaled to…
Explore lesson ChemistryLessonEnthalpy of Formation Cycles
An enthalpy of formation table gives a value for making each compound from its elements in their reference states. A reaction may not start from elements, but Hess's law allows…
Explore lesson ChemistryLessonEnthalpy of Neutralisation
Neutralising an aqueous acid with a base often warms the solution. For dilute strong acids and strong bases, the molar heat per mole of water formed is often near −57 kJ mol⁻¹…
Explore lesson ChemistryLessonEnthalpy of Phase Changes
Changing a substance's phase changes its enthalpy even when its chemical formula stays the same. Melting, vaporization and sublimation usually absorb heat at the transition…
Explore lesson ChemistryLessonEnthalpy of Solution and Dilution
Dissolving a substance can warm or cool a solution. The observed heat reflects disruption of solute and solvent interactions and formation of new solute–solvent interactions. The…
Explore lesson ChemistryLessonEntropy and Energy Dispersal
Entropy helps explain why energy and matter tend to spread among available possibilities. It is often introduced as “disorder,” but that word can be vague or misleading. A better…
Explore lesson ChemistryLessonEntropy and Gibbs-Energy Calculations
An exothermic reaction is not automatically favoured at every temperature, and an endothermic process can be favoured when entropy increases sufficiently. Gibbs energy combines…
Explore lesson ChemistryLessonEntropy and Gibbs-Energy Formulae
An exothermic reaction is not automatically favorable under every condition, and an endothermic process can occur spontaneously. Gibbs energy combines enthalpy and entropy at a…
Explore lesson ChemistryLessonEntropy Change of the Surroundings
The second law concerns a system together with its surroundings. A reaction can make the system more ordered yet proceed because the heat it releases increases the surroundings'…
Explore lesson ChemistryLessonEnvironment and Sustainability Map
Environmental chemistry follows substances beyond the reaction flask. A design choice changes feedstock use, emissions, product performance and disposal. A harmful property…
Explore lesson ChemistryLessonEnvironmental and Safety Context
Organohalides range from useful synthesis intermediates to substances that require strict control because of toxicity, volatility, or environmental persistence. A carbon–halogen…
Explore lesson ChemistryCollectionEnvironmental Chemistry
Study Environmental Chemistry with 30 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonEnvironmental Chemistry as a Systems Science
A pollutant released from a chimney does not stay put. It mixes into the air, reacts, dissolves in rain, settles onto soil, is washed into rivers and may end up in fish or…
Explore lesson ChemistryLessonEnvironmental Chemistry Reference Values
Environmental chemistry tables can look deceptively simple: pollutant name, number and unit. Yet a useful value also needs the authority, jurisdiction, date, medium, averaging…
Explore lesson ChemistryLessonEnvironmental Chemistry Terms
Environmental chemistry follows substances through air, water, soil, organisms and human activity. The vocabulary matters because a chemical's presence is not the same as…
Explore lesson ChemistryLessonEnvironmental Chemistry: Unit Review
The atmosphere, waters, soil and organisms are connected parts of one chemical system. An emitted gas may oxidize in air, dissolve in rain, react in a stream and eventually sorb…
Explore lesson ChemistryLessonEnvironmental Effects of Metallurgy
Metal extraction supplies useful materials while moving large amounts of rock, using energy and producing residual streams. Environmental effects depend on the ore, process and…
Explore lesson ChemistryLessonEnzyme Catalysis
Enzymes achieve impressive reaction rates under comparatively mild biological conditions. They share the catalyst principle of providing a faster route without shifting…
Explore lesson ChemistryLessonEnzyme Inhibition Kinetics
Many drugs, poisons and natural regulators work by slowing enzymes. How they do so leaves a kinetic signature. By measuring initial rates at several substrate and inhibitor…
Explore lesson ChemistryLabEnzyme kinetics
Enzymes bind substrate and release product. Watch the rate level off as enzymes get busy.
Explore lesson ChemistryLessonEnzyme-Inspired Catalyst Design
Enzymes achieve selective chemistry partly by shaping the environment around an active site. A metal's directly bonded ligands matter, but nearby amino acids, water channels and…
Explore lesson ChemistryLessonEnzymes as Biological Catalysts
Enzymes accelerate reactions in living systems while remaining available for further catalytic cycles. Their structured active sites bind particular substrates and create…
Explore lesson ChemistryLessonEnzymes as Protein Catalysts
An enzyme's sequence matters because folding places selected amino-acid side chains around a substrate. Some enzymes also require a metal ion or organic cofactor; others are…
Explore lesson ChemistryLessonEpoxide Formation
A peroxyacid can transfer an oxygen atom to an alkene to form an epoxide, a three-membered ring containing the two former double-bond carbons and one oxygen. The carbon–carbon…
Explore lesson ChemistryLessonEpoxide Ring Opening
Epoxides are ethers, but their three-membered rings are much more reactive than ordinary open-chain ethers. A nucleophile can break one C–O bond and relieve ring strain, leaving…
Explore lesson ChemistryLessonEpoxides as Cyclic Ethers
An epoxide is a three-membered ring containing one oxygen and two carbons. It is an ether by connectivity, but its small ring is strained and much more reactive toward…
Explore lesson ChemistryLessonEPR of Organic Radicals
Organic radicals appear as reaction intermediates, in polymers, in biological electron transfer and in materials such as organic semiconductors. Their g values lie very close to…
Explore lesson ChemistryLessonEPR of Transition-Metal Complexes
For inorganic and bioinorganic chemists, EPR is one of the most direct probes of a metal centre. Only paramagnetic states are detected, so the spectrum immediately filters out…
Explore lesson ChemistryLessonEPR Worked Interpretation
An EPR spectrum is not just a set of peaks to label. Its field position, splitting and line shape each answer a different question about an unpaired electron. The field position…
Explore lesson ChemistryLessonEqual Masses Can Give Unequal Reaction Amounts
Equal masses of two substances rarely contain equal numbers of particles. Even if they did, a reaction might require them in an unequal mole ratio. Limiting-reagent questions…
Explore lesson ChemistryLabEquation balancer
Type any unbalanced equation; it is balanced exactly, with every reasoning step shown.
Explore lesson ChemistryLessonEquation Coefficients as Mole Ratios
A balanced equation can supply several valid ratios. The useful ratio depends on which species is given and which is wanted. Selecting, labeling and orienting the appropriate…
Explore lesson ChemistryLessonEquations in Industry and Everyday Life
Chemical equations help explain a kitchen rising agent, a fuel burner, a cement kiln and a water-treatment tank. Each equation tracks atoms through a specific chemical change.…
Explore lesson ChemistryLessonEquilibrium and Gibbs Energy
The reaction quotient predicts direction, while Gibbs energy expresses the thermodynamic driving force. These views are connected: current composition enters through Q, and the…
Explore lesson ChemistryLessonEquilibrium Constant from an ICE Table
Many equilibrium problems give you the starting mixture and just one piece of information about the final state: the amount of a product formed, the fraction of a reactant left…
Explore lesson ChemistryLessonEquilibrium Constant from Standard EMF
Standard cell potential tells more than initial electrical driving force. Together with the electron number n, it determines the equilibrium constant of the overall cell reaction…
Explore lesson ChemistryLessonEquilibrium Constants and Reversed Reactions
An equilibrium constant belongs to a specific balanced reaction as written. Reversing the arrow or multiplying every coefficient changes the expression and therefore changes the…
Explore lesson ChemistryLessonEquilibrium Constants from Partition Functions
Classical thermodynamics tells us that an equilibrium constant is fixed by the standard reaction Gibbs energy, K = exp(−Δ_rG°/RT), but it says nothing about *why* Δ_rG° has the…
Explore lesson ChemistryLessonEquilibrium Graphs and Data
Equilibrium graphs reveal behavior that equations alone can hide. A concentration-time plot can distinguish an immediate addition from a later reaction adjustment, while a…
Explore lesson ChemistryLessonEquilibrium Misconceptions and Checks
Equilibrium answers can be numerically tidy yet chemically wrong. Common failures include reversing a quotient, inserting pure solids into K, using a buffer formula after a…
Explore lesson ChemistryLessonEquilibrium Numerical Review
Equilibrium problems share a structure: a balanced equation, a table, a K expression and some algebra. The same structure means the same mistakes recur. Rather than learning a…
Explore lesson ChemistryLessonEquilibrium Yield with a Limiting Feed
Stoichiometry tells you the most product a reaction could possibly give: the limiting reactant runs out and the reaction stops. Equilibrium tells you something different: a…
Explore lesson ChemistryCollectionEquilibrium: Chemical and Ionic
Study Equilibrium: Chemical and Ionic with 65 free lessons, worked examples, and answered practice questions.
Explore lesson ChemistryLessonEquilibrium: Chemical and Ionic Review
Chemical and ionic equilibria use the same central principle: for a written reaction at fixed temperature, activities adjust until Q equals K. What changes from one problem to…
Explore lesson ChemistryLessonEquivalent Concept in Redox
The equivalent concept compresses redox stoichiometry into electron-transfer capacity. If one formula unit accepts or releases n electrons in a specified reaction, one mole of…
Explore lesson ChemistryLessonEquivalent Protons and Number of Signals
The first question to ask of any ¹H NMR spectrum is simple: how many signals are there? Each signal corresponds to one proton environment — a set of hydrogen atoms that…
Explore lesson ChemistryLessonError Checks in Solution Calculations
Solution problems combine several easily swapped bases: grams versus moles, solvent versus solution, and initial versus final volume. A correct-looking formula can still give a…
Explore lesson ChemistryLabErrors and calibration
A calibration line: fit standards, check the residuals, and find an unknown with its uncertainty.
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