Thermochemistry & Thermodynamics — 60 Terms Defined

Gibbs Free Energy Thermochemistry & Thermodynamics kJ/mol The thermodynamic potential whose change determines whether a process is spontaneous at constant temperature and pressure. ΔG = ΔH − TΔS

Gibbs–Helmholtz Equation Thermochemistry & Thermodynamics kJ/mol The relation showing how the Gibbs free energy of a system varies with temperature. (∂(ΔG/T)/∂T)_p = −ΔH/T²

Heat Thermochemistry & Thermodynamics J Energy transferred between a system and its surroundings solely because of a temperature difference. q = mcΔT

Heat Capacity at Constant Pressure Thermochemistry & Thermodynamics J/(mol·K) The heat needed to raise a system's temperature by one kelvin while pressure is held constant. C_p = C_V + R (ideal gas)

Heat Capacity at Constant Volume Thermochemistry & Thermodynamics J/(mol·K) The heat needed to raise a system's temperature by one kelvin while its volume is held fixed. C_V = (∂U/∂T)_V

Helmholtz Free Energy Thermochemistry & Thermodynamics kJ/mol The thermodynamic potential that determines spontaneity at constant temperature and volume. A = U − TS

Hess's Law Thermochemistry & Thermodynamics kJ/mol 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

Internal Energy Thermochemistry & Thermodynamics J The total kinetic and potential energy of all the particles within a system. ΔU = q + w

Irreversible Process Thermochemistry & Thermodynamics J/K A real process that passes through non-equilibrium states and cannot be reversed without leaving a permanent change in the surroundings. ΔS_universe > 0

Isobaric Process Thermochemistry & Thermodynamics J A process carried out at constant pressure. q_p = ΔH

Isochoric Process Thermochemistry & Thermodynamics J A process carried out at constant volume, so that no expansion work is done. w = 0, q_V = ΔU

Isolated System Thermochemistry & Thermodynamics Dimensionless A system that exchanges neither energy nor matter with its surroundings. ΔU = 0

Isothermal Process Thermochemistry & Thermodynamics J A process carried out at constant temperature, with heat exchanged as needed to maintain it. ΔU = 0 (ideal gas), w = −nRT ln(V₂/V₁)

Kirchhoff's Law Thermochemistry & Thermodynamics kJ/mol The relation describing how the enthalpy change of a reaction varies with temperature. ΔH(T₂) = ΔH(T₁) + ΔC_p(T₂ − T₁)

Maximum Work Thermochemistry & Thermodynamics J The greatest amount of work obtainable from a change of state, achieved only along a reversible path. w_max = ΔA; w_max(non-pV) = ΔG

Molar Heat Capacity Thermochemistry & Thermodynamics J/(mol·K) The heat required to raise the temperature of one mole of a substance by one kelvin. C_m = q / (nΔT)

Open System Thermochemistry & Thermodynamics Dimensionless A system that can exchange both energy and matter with its surroundings.

Path Function Thermochemistry & Thermodynamics J A quantity whose value depends on the specific route taken between two states. δq, δw

Reversible Process Thermochemistry & Thermodynamics J An idealised process carried out through a continuous series of equilibrium states, so it can be reversed by an infinitesimal change. w_rev = −∫p dV

Second Law of Thermodynamics Thermochemistry & Thermodynamics J/K The total entropy of the universe increases in every spontaneous process. ΔS_universe > 0

Specific Heat Capacity Thermochemistry & Thermodynamics J/(kg·K) The heat required to raise the temperature of one kilogram of a substance by one kelvin. c = q / (mΔT)

Spontaneity Thermochemistry & Thermodynamics kJ/mol The tendency of a process to occur without any continuous external input of energy. ΔG < 0

Standard Enthalpy of Combustion Thermochemistry & Thermodynamics kJ/mol The enthalpy change when one mole of a substance burns completely in excess oxygen under standard conditions. ΔH_c°

Standard Enthalpy of Formation Thermochemistry & Thermodynamics kJ/mol The enthalpy change when one mole of a compound forms from its elements in their standard states. ΔH_f°