Chemistry

Thermo, equilibrium, kinetics

Enthalpy, Gibbs energy, K, and rate laws.

Basics

Enthalpy

Heat at constant pressure tracks ΔH. ΔH<0 is exothermic; ΔH>0 is endothermic. Hess’s law: overall ΔH is path-independent and equals the sum of steps.

Gibbs energy

At constant T and P, a process is spontaneous if ΔG<0. ΔG = ΔH − TΔS. At equilibrium ΔG=0 and ΔG° = −RT ln K.

Le Chatelier

A stress (concentration, pressure, temperature) shifts equilibrium to reduce that stress. A catalyst does not change K; it speeds both directions.

Formulas

Gibbs energy

ΔG = ΔH − TΔS

Enthalpy and entropy compete. At high T, TΔS grows.

Symbols

ΔG change in Gibbs energy
ΔH enthalpy change
ΔS entropy change
T absolute temperature

Standard Gibbs and K

ΔG° = −RT ln K

K>1 favors products; K<1 favors reactants.

Symbols

K equilibrium constant
R gas constant

Concentration equilibrium constant

aA + bB ⇌ cC + dD, K_c = ([C]ᶜ[D]ᵈ) / ([A]ᵃ[B]ᵇ)

Pure solids and liquids are usually omitted (activity 1). Gases may use K_p.

Symbols

a,b,c,d stoichiometric coefficients

Arrhenius equation

k = A e^{−E_a / RT}

A high barrier or low T makes the rate constant small.

Symbols

k rate constant
A pre-exponential factor
E_a activation energy

Rate law (example)

rate = k [A]ᵐ [B]ⁿ

Orders m and n are experimental, not taken from coefficients.

Symbols

m, n reaction orders

In this field

Chemistry

Atoms and the periodic table

Atomic structure, nucleus and electrons, periods and groups.

Chemistry

Chemical bonding

Ionic, covalent, and metallic bonds, plus molecular shape.

Chemistry

The mole and stoichiometry

Moles, molar mass, empirical formulas, and yield.

Chemistry

Gases and acids–bases

Ideal gas, pH, and buffers.

Chemistry

Electrochemistry and organic basics

Oxidation numbers, cells, Nernst, functional groups.

Chemistry

Nuclear chemistry

Radioactivity, half-life, binding energy.

Chemistry

Solutions and kinetics

Concentration, colligative properties, rate laws.

Chemistry

Analytical chemistry

Titration, spectroscopy, and chromatography — measuring what is present and how much.

Chemistry

Polymers and solids

Crystals and glasses, metal–ionic–covalent solids, polymer chains and the glass transition.

Chemistry

Coordination compounds

Ligands, coordination number, crystal field, colour, and an 18-electron sketch.

Chemistry

Electrochemical cells

Galvanic versus electrolytic, Nernst, Faraday, and a corrosion sketch.

Chemistry

Phase equilibria and diagrams

Gibbs phase rule, unary diagrams, eutectics, and the lever rule.