Thermo Lecture 4

Question 1

What is the equation for internal energy U (for constant composition)?

Answer 1

dU = TdS - PdV

Question 2

What is the ‘Entropy Max’ & ‘Energy Min’ principle?

Answer 2

For an isolated system in equilibrium, S is at a maximum. For a closed system at equilibrium, U is at a minimum. When equilibrium is reached, thermodynamic potentials are at a minimum.

Question 3

Give the equation for Gibbs Free energy, G. What is it?

Answer 3

G = H - TS

A measure of the available enthalpy to do work

Question 4

Give the equation for dG

Answer 4

dG = VdP - SdT

Question 5

When is chemical equilibrium achieved?

Answer 5

When G is at its minimum value

Question 6

What is required for a reaction to proceed spontaneously?

Answer 6

ΔGr < 0

A reaction will proceed in a direction that minimises G

Question 7

How can we calculate G>

Answer 7

1. G0 = G0(Pref, Tref) - ∫SdT + ∫V dP
   Between T and Tref and P and Pref
2. ΔGr = ΣviGi

Question 8

How do you calculate the volume when mixing two volumes?

Answer 8

V = Σvi ni

Where vi is the partial molar volume

Question 9

What is the partial molar volume?

Answer 9

The change in volume of a whole solution as a function of the change of moles of species 1 when the number of moles of species 2 is held constant.

Question 10

What is the partial molar Gibbs Free Energy?

Answer 10

The Chemical Potential, μ

Question 11

What is the equation for μ

Answer 11

μi = (dGi/dni)T,P,nj