Lecture 3

Question 1

Give the equation for the ΔsurrS at constant pressure

Answer 1

ΔS= -ΔH/T
as at constant pressure
q system= ΔH

Question 2

Give the equation for entropy change of a reaction

Answer 2

ΔS =∑ vS (products) - ∑ vS (reactants)

Question 3

Give the equation for ΔS total

Answer 3

ΔStotal = ΔS system + ΔS surroundings

Question 4

How do you calculate ΔS system?

Answer 4

Sm for the final substance minus Sm for initial substance

Question 5

How can you predict the ΔS of a reaction?

Answer 5

• look at the difference in the number of gaseous moles
• increasing means that disorder has increased so ΔS is greater
• if gaseous moles stay the same then ΔS is small

Question 6

Give the equation for ΔG

Answer 6

ΔG = ΔH - TΔS

Question 7

What is the ΔG for a spontaneous change?

Answer 7

for a spontaneous change;
ΔG < 0 (at constant temp and pressure)

Question 8

If ΔH and ΔS are negative;
- what is ΔG?
- is it spontaneous?

Answer 8

• ΔG depends on T
• whether it is spontaneous depends on T

Question 9

If ΔH is negative and ΔS is positive;
- what is ΔG?
- is it spontaneous?

Answer 9

• ΔG is negative
• it is spontaneous

Question 10

If ΔH is positive and ΔS is negative;
- what is ΔG?
- is it spontaneous?

Answer 10

• ΔG is positive
• its not spontaneous

Question 11

If ΔH and ΔS are positive;
- what is ΔG?
- is it spontaneous?

Answer 11

• ΔG depends on T
• whether its spontaneous depends on T