enthalpy and entropy

Question 1

What is entropy?

Answer 1

A measure of the dispersal of energy in a system OR how disordered something is.

Question 2

What is a spontaneous process?

Answer 2

A process that proceeds on its own without external influence (so no continuous energy supply).
Eg, diffusion.

Question 3

Why can some endothermic reactions still be feasible?

Answer 3

As these substances become more energetically stable when there is disorder.

Question 4

When is a substance thermodynamically stable?

Answer 4

When it reaches its maximum entropy state (lowest energy state).

Question 5

How is entropy change (ΔS⦵) calculated? What is it measured in? And what does it being +ve and -ve mean?

Answer 5

● ΔS⦵ = ΣS⦵products - ΣS⦵reactants
● Measured in JK-1mol-1
● +ve means increase in disorder/entropy. ● -ve means decrease in disorder/entropy.
S⦵ alone is the entropy per molecule which is always positive.

Question 6

What is the Gibbs free energy equation? What are
the outcomes

Answer 6

ΔG = ΔH - TΔS

ΔG < 0 ⇒ feasible (more negative ⇒ more feasible).
● ΔG = 0 ⇒ equilibrium (this is similar for a puddle in
equilibrium).
● ΔG > 0 ⇒ not feasible.
Note that ΔS can be in JK-1mol-1 rather than kJK-1mol-1.

Question 7

When is Gibbs free energy not useful

Answer 7

While a reaction may be feasible, it can still…
● Have a very high activation energy.
● Be incredibly slow that you won’t it happening at all.

Question 8

How can Gibbs free energy be plotted? What does the gradient tell you?

Answer 8

● Plot the ΔG v T of ΔG = ΔH - TΔS as y = mx + c. ● The gradient tells you the entropy change.
You can see when a reaction becomes feasible under this.