Entropy and Gibbs' Free Energy

Question 0

What is the equation for ΔG?

Answer 0

ΔG = ΔH - TΔS where the units are kelvin and joules

Question 1

What is the equation for ΔS(total)?

Answer 1

ΔS(total) = ΔS(system) + ΔS(surroundings) = ΔS(system) - (ΔH/T) where the units are kelvin and joules

Question 2

When ΔH is -ve and ΔS is +ve, what is ΔG and is the reaction feasible?

Answer 2

ΔG is always -ve and the reaction is feasible

Question 3

When ΔH is +ve and ΔS is -ve, what is ΔG and is the reaction feasible?

Answer 3

ΔG is always +ve and the reaction is never feasible

Question 4

When ΔH is -ve and ΔS is -ve, what is ΔG and is the reaction feasible?

Answer 4

ΔG is -ve at low temperatures and the reaction is feasible at low temperatures

Question 5

When ΔH is +ve and ΔS is +ve, what is ΔG and is the reaction feasible?

Answer 5

ΔG is -ve at high temperatures and the reaction is feasible at high temperatures

Question 6

What is the definition of ‘free energy change (ΔG)’?

Answer 6

It’s the balance between enthalpy, entropy and temperature for a process i.e. ΔG = ΔH - TΔS

Question 7

A reaction is feasible when ΔG…

Answer 7

<0

Question 8

A reaction is feasible when ΔS(total)…

Answer 8

> 0 i.e. ΔS(total)>0

Question 9

Define the standard conditions.

Answer 9

298K/25°C and 101kPa/1atm

Question 10

What is the equation for ΔS(system)?

Answer 10

ΔS(system) = ΣΔS(products) - ΣΔS(reactants)

Question 11

Regarding ΔG, as temperature increases, energy derived from ΔS becomes ____ significant.

Answer 11

more

Question 12

Generally, most exothermic reactions are spontaneous even if ΔS decreases because ΔH contributes ____ to ΔG than ΔS does.

Answer 12

more; the exceptions are reactions ocurring at high T where ΔS decreases

Question 13

A reaction may be thermodynamically feasible but may not appear to have occured because…

Answer 13

the reaction has too high an activation energy and the reaction may be too slow to be observed.