Thermodynamics: physical equilibrium

Question 1

Define a phase

Answer 1

A phase is a state of matter that is uniform throughout, in both chemical composition and in physical state

P is the number of phases in a system

Question 2

Define a constituent

Answer 2

A constituent is a chemical species (an ion or molecule) that is present in the system

Question 3

Define a component

Answer 3

A component is a chemically independent constituent of a system. C = the number of components in a system

Note: C = 2 –> a binary mixture

C = 3 –> a ternary mixture

Question 4

Describe Gibb’s phase rule

Answer 4

F = C - P + 2

F is the variance ie degrees of freedom, P is the number of phases and C is the number of components

If F = 0, we cannot vary anything

If F = 1, we can vary p or T

If F = 2, we can vary p and T independently

Question 5

Define and describe the temperature dependence of free energy

Answer 5

S_m > 0 for all substances.

The phase with the lowest free energy at a given T is the most stable one.

Two phases have the same free energy at a transition temperature

Question 6

Define and describe the pressure dependence of the free energy

Answer 6

V_m > 0 for all substances

Two phases have the same free energy at a transition pressure

Question 7

Describe phase boundaries

Answer 7

At a phase boundary, the free energies of two coexisting phases are equal.

It follows that dG_m(1) = dG_m(2)

Question 8

Derive and explain the Clapeyron equation

Answer 8

Note that all phase boundaries have positive slopes.

Question 9

Derive the Clausius-Claperyron equation

Answer 9

Question 10

Draw out and describe the experimental setup for measuring Δ_VapH_m

Answer 10

Question 11

Define a critical point

Answer 11

A critical point ends a liquid-gas phase boundary