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Thermochemistry & Thermodynamics

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Thermochemistry & Thermodynamics

Standard Molar Entropy

The absolute entropy of one mole of a substance in its standard state at 298 K.

ΔS° = ΣS°(products) − ΣS°(reactants) J/(mol·K)
Thermochemistry & Thermodynamics

Standard State

The reference condition of a pure substance at 1 bar pressure and a stated temperature, conventionally 298.15 K.

denoted by ° Dimensionless
Thermochemistry & Thermodynamics

State Function

A property whose value depends only on the current state of the system, not on how that state was reached.

ΔX = X_final − X_initial Various
Thermochemistry & Thermodynamics

Surroundings

Everything outside the chosen system with which it can exchange energy or matter.

Dimensionless
Thermochemistry & Thermodynamics

System

The specific part of the universe chosen for thermodynamic study, separated from everything else by a real or imaginary boundary.

Dimensionless
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
Thermochemistry & Thermodynamics

Thermodynamic Equilibrium

The state in which a system's properties no longer change with time and all driving forces are balanced.

ΔG = 0 kJ/mol
Thermochemistry & Thermodynamics

Thermodynamics

The branch of science dealing with energy, its transformations, and the direction in which processes occur.

J
Thermochemistry & Thermodynamics

Third Law of Thermodynamics

The entropy of a perfect crystalline substance approaches zero as the temperature approaches absolute zero.

S → 0 as T → 0 K J/(mol·K)
Thermochemistry & Thermodynamics

Trouton's Rule

The empirical observation that the entropy of vaporisation of many liquids is close to 88 J/(mol·K) at their boiling point.

ΔS_vap = ΔH_vap / T_b ≈ 88 J/(mol·K)
Thermochemistry & Thermodynamics

Work

Energy transferred when a force moves through a distance, most often in chemistry as a gas expanding against external pressure.

w = −p_ext ΔV J
Thermochemistry & Thermodynamics

Zeroth Law of Thermodynamics

If two systems are each in thermal equilibrium with a third, they are in thermal equilibrium with each other.

T_A = T_C and T_B = T_C ⟹ T_A = T_B K