Thermodynamics

Question 1

What are the three factors that determine whether a reaction is feasible or not?

Answer 1

• temperature
• entropy change
• enthalpy change

Question 2

What is the equation for Gibb’s free energy?

Answer 2

ΔG = ΔH - TΔS

Question 3

What are the SI units for the Gibb’s free energy calculation?

Answer 3

ΔG = Gibb’s free energy (kJmol-1)
ΔH = Enthalpy change (kJmol-1)
T = temperature (K)
ΔS = Entropy change (kJK-1mol-1)

Question 4

When is a reaction classed as feasible?

Answer 4

when ΔG is less than or equal to 0

Question 5

When ΔH is negative and ΔS is positive what does this mean about the reaction?

Answer 5

reaction is always feasible

Question 6

When ΔH is positive and ΔS is negative what does this mean about the reaction?

Answer 6

reaction is never feasible

Question 7

When ΔH is negative and ΔS is negative what does this mean about the reaction?

Answer 7

reaction is feasible at low temperatures

Question 8

When ΔH is positive and ΔS is positive what does this mean about the reaction?

Answer 8

reaction is feasible at high temperatures

Question 9

What does entropy mean?

Answer 9

the level of disorder

Question 10

What is the SI units of entropy?

Answer 10

JK-1mol-1

Question 11

Which state of matter has the highest level of disorder (highest entropy)?

Answer 11

gas

Question 12

How can you increase disorder?

Answer 12

• increasing the number of particles
• changing state from solid -> liquid -> gas

Question 13

What is the equation for entropy?

Answer 13

ΔS = standard entropy of products - standard entropy of reactants

Question 14

How do you calculate temperature when a reaction becomes feasible (ΔG = 0)

Answer 14

T (in Kelvin) = ΔH/ΔS