Thermodynamics

Question 1

Boyle’s Law

Answer 1

p ∝ 1/V

Question 2

Lussac’s Law

Answer 2

V ∝ T (in K)

Question 3

Charles’ Law

Answer 3

p ∝ T

Question 4

The ideal gas Law

Answer 4

pV = nRT

Question 5

1 bar in Pascals or N m^(-2)

Answer 5

1 x 10^5 N m^(-2)

Question 6

Converting from °C into K

Answer 6

+ 273.15

Question 7

For 2 gases A and B, what are their partial pressures?

Answer 7

PA = (nA RT) / V
PB = (nB RT) / V

Total pressure = PA + PB

Question 8

Assumptions for the ideal gas Law

Answer 8

The molecules take up no volume

No interactions between molecules

Question 9

Van der Waals equation of state and what a and b account for

Answer 9

(nRT / V - nb) - (an^2 / V^2)
a corrects for attractive interactions, which would reduce the pressure from an ideal gas
b corrects for volume of molecules, which would increase the pressure from an ideal gas

Question 10

ΔU =

Answer 10

Internal energy change

Question 11

Internal energy =

Answer 11

U(translation) + U(rotation) + U(vibration) + U(electronic)

For an ideal gas we only need to consider U(translation)

Question 12

The Equipartition principle

Answer 12

for each degree of freedom, we get 0.5kT of energy (0.5 RT per mol)
U = 3/2 R

Question 13

1st Law of thermodynamics

Answer 13

ΔU = q + w

Question 14

What does isochoric mean?

Answer 14

Constant volume

–> dV = 0

Question 15

What does isobaric mean?

Answer 15

Constant pressure
(1st law unchanged)

Question 16

What does adiabatic mean?

Answer 16

No heat change

–> Δq = 0

Question 17

What does isothermal mean?

Answer 17

Potential and kinetic energy are unchanged

• -> ΔU = 0 for an ideal gas
• -> 𝛿U / 𝛿V = 0 (partial derivatives)

Question 18

H =

Answer 18

U + pV

Question 19

2nd Law of thermodynamics

Answer 19

The entropy change of a system and surroundings increases in the course of spontaneous change
ΔS(tot) > 0

Question 20

Trouton’s Rule

Answer 20

The entropy change when a liquid is vaporised:

Δ(vap)S ≈ 85 J K^-1 mol^-1 for most liquids

Question 21

Sign of ΔS for solid –> ions

Answer 21

Negative (ions are more ordered)

Question 22

3rd Law of thermodynamics

Answer 22

A perfect crystal at 0 K has zero entropy

Question 23

Free energies and when they’re appropriate

Answer 23

Gibbs: G = H - TS (for constant P)
Helmholtz: A = U - TS (for constant V)

Question 24

dU =

Answer 24

dq + dw = TdS - pdV