Chapter 3 - The Second Law

Second Law of Thermodynamics

No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work

Entropy (S)

A measure of the energy dispersed in a process

Boltzmann formula

The entropy calculated from it is sometimes called the statistical entropy

Reversible isothermal expansion from A to B at Th

The entropy change is qh/Th, where qh is the energy supplied to the system as heat from the hot source

Reversible adiabatic expansion from B to C

No energy leaves the system as heat, so the change in entropy is zero

Reversible isothermal compression from C to D at Tc

Energy is released as heat to the cold sink; the change in entropy of the system is qc/Tc; in this expression qc is negative

Reversible adiabatic compression from D to A

No energy enters the system as heat, so the change in entropy is zero

Efficiency (ε)

Clausius inequality

Expansion

Thermodynamic temperature scale

The efficiency of a heat engine

Trouton's rule

A wide range of liquids give approximately the same standard entropy of vaporization, about 85 J K^-1 mol ^-1

Third Law of thermodynamics

The entropy of all perfect crystalline substances is zero at T = 0

Nernst heat theorem

The entropy change accompanying any physical or chemical transformation approaches zero as the temperature approaches zero: ΔS → 0 as T → 0 provided all the substances involved are perfectly crystalline.

Third-Law entropies

Entropies reported on the basis that S(0) = 0

Standard (Third-Law) entropy

S°(T)

Standard reaction entropy

The difference between the molar entropies of the pure, separated products and the pure, separated reactants, all substances being in their standard states at the specified temperature

Helmholtz energy (A)

Maximum work

The change in the Helmholtz function

Gibbs energy (G)

Standard Gibbs energy of reaction

The combination of standard entropies and enthalpies of reaction

Standard Gibbs energies of formation

The standard reaction Gibbs energy for the formation of a compound from its elements in their reference states

Fundamental equation

Maxwell relations

Thermodynamic equation of state

Properties of the Gibbs energy

First relation

* G always decreases when the temperature is raised
* G decreases most sharply when the entropy of the system is large.

Second relation

* G always increases when the pressure of the system is increased.
* G is more sensitive to pressure when the volume of the system is large.

Gibbs-Helmholtz equation