Introduction to Thermodynamics

U = internal energy

Entropy P P / 2

(Craig Counterman)

J g-1 K-1 at 300 K atomic number (Craig Counterman)

Allotropic Transition

Q Why is Gibbs free energy called ‘free’? A Because it is that part of the energy which is in principle obtainable as mechanical work. N. K. Adam, Physical Chemistry, Clarendon Press, Oxford (1956) page 263.

Allotropic Transition in Pure Iron

Mechanical Mixture Gibbs free energy per mole Concentration x of B m free energy of mechanical m o mixture B G* m o Gibbs free energy per mole A x 1-x A B Concentration x of B

entropy is a capacity property, like mass, energy etc entropy is a capacity property, like mass, energy etc. Different entropies can be added: S1+S2=S3 How does this fit with the probability picture?

Entropy w=1 P w=very large P / 2

w is not a capacity property of the system. For example, the chance of throwing two sixes with dice is (1/6)2, not 1/6+1/6. Boltzmann realised that we should use ln{w} and not w to meaure disorder.

Gibbs free energy per mole free energy of mechanical m o mixture B G* Gibbs free energy per mole m o A ∆G M G{x} free energy of solution A B x Composition

Gibbs free energy per mole A m { } 1-x A m { } x B G{x} A B x Composition

Binary solution

Irreversible Processes: Steady State

dissipating free energy

Process whose direction can be changed by an infinitesimal change in external conditions is reversible.

Process which dissipates energy is irreversible to an infinitesimal change in external conditions.