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Thermochemistry & Thermodynamics

Enthalpy

A thermodynamic state function equal to internal energy plus the product of pressure and volume.

H = U + pV kJ/mol Thermochemistry & Thermodynamics

Enthalpy Level Diagram

A diagram plotting the enthalpies of reactants and products to show the direction and size of the enthalpy change.

kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Atomisation

The enthalpy change when one mole of gaseous atoms is produced from an element in its standard state.

ΔH_at° kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Dilution

The enthalpy change when a solution is diluted from one concentration to another by adding solvent.

ΔH_dil kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Fusion

The enthalpy change when one mole of a solid melts to a liquid at its melting point.

ΔH_fus kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Neutralisation

The enthalpy change when an acid and a base react to form one mole of water under standard conditions.

H⁺ + OH⁻ → H₂O, ΔH = −57.1 kJ kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Reaction

The heat absorbed or released when a reaction occurs at constant pressure in the molar amounts of the balanced equation.

ΔH_rxn = ΣΔH_f(products) − ΣΔH_f(reactants) kJ/mol Solutions & Colligative Properties

Enthalpy of Solution

The heat absorbed or released when one mole of a substance dissolves completely in a large excess of solvent.

ΔH_sol = ΔH_lattice + ΔH_hyd kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Sublimation

The enthalpy change when one mole of a solid converts directly into vapour.

ΔH_sub = ΔH_fus + ΔH_vap kJ/mol Thermochemistry & Thermodynamics

Enthalpy of Vaporisation

The enthalpy change when one mole of a liquid becomes vapour at its boiling point.

ΔH_vap kJ/mol Thermochemistry & Thermodynamics

Bond Dissociation Enthalpy

The enthalpy change when one mole of a specific bond is broken homolytically in the gas phase.

A–B(g) → A·(g) + B·(g) kJ/mol Thermochemistry & Thermodynamics

Standard Enthalpy of Combustion

The enthalpy change when one mole of a substance burns completely in excess oxygen under standard conditions.

ΔH_c° kJ/mol Thermochemistry & Thermodynamics

Standard Enthalpy of Formation

The enthalpy change when one mole of a compound forms from its elements in their standard states.

ΔH_f° kJ/mol Stoichiometry & Chemical Reactions

Endothermic Reaction

A reaction that absorbs energy from the surroundings, giving a positive enthalpy change.

ΔH > 0 kJ/mol Stoichiometry & Chemical Reactions

Exothermic Reaction

A reaction that releases energy to the surroundings, giving a negative enthalpy change.

ΔH < 0 kJ/mol Thermochemistry & Thermodynamics

Hess's Law

The total enthalpy change of a reaction is the same regardless of the route taken, provided the initial and final states are identical.

ΔH_total = ΣΔH_steps kJ/mol Thermochemistry & Thermodynamics

Kirchhoff's Law

The relation describing how the enthalpy change of a reaction varies with temperature.

ΔH(T₂) = ΔH(T₁) + ΔC_p(T₂ − T₁) kJ/mol Thermochemistry & Thermodynamics

Thermochemical Equation

A balanced chemical equation that also states the enthalpy change for the amounts shown.

aA + bB → cC, ΔH = x kJ kJ/mol Acids, Bases & Salts

Arrhenius Theory

The theory defining an acid as a substance that produces H⁺ ions in water and a base as one that produces OH⁻ ions.

HA → H⁺ + A⁻; BOH → B⁺ + OH⁻ Dimensionless Thermochemistry & Thermodynamics

Bomb Calorimeter

A rigid sealed vessel used to measure the heat released by combustion at constant volume.

q_V = ΔU J Inorganic & Coordination Chemistry

Chelate Effect

The greater stability of a complex containing a multidentate ligand compared with one containing equivalent monodentate ligands.

ΔS favourable kJ/mol Solutions & Colligative Properties

Cryoscopic Constant

The freezing point depression produced by a one-molal solution of a non-electrolyte in a given solvent.

K_f = RT_f²M / ΔH_fus K·kg/mol States of Matter & Gas Laws

Deposition

The direct conversion of a vapour into a solid without an intermediate liquid phase.

kJ/mol Solutions & Colligative Properties

Ebullioscopic Constant

The boiling point elevation produced by a one-molal solution of a non-electrolyte in a given solvent.

K_b = RT_b²M / ΔH_vap K·kg/mol