Chapter 18

Question 1

3rd Law of Thermodynamics

Answer 1

the Entropy of a pure, perfectly ordered crystalline solid at 0 ̊K is zero.

Question 2

What are the 4 entropy rules of thumb?

Answer 2

a.) The entropy of a substance increases going from a solid to a liquid to a gas.
b.) Entropy increases with increasing numbers of moles (molecules, ions, atoms …)
c.) Gas escaping from a solution increases the entropy of the system.
d.) Entropy of a pure substance, liquid or solid, increases when dissolved in a solvent
as long as there are no strong interactions between the solvent and solute.

Question 3

Gibbs Free Energy

Answer 3

∆G = ∆H - T ∆S

Question 4

∆Gsystem < 0

Answer 4

reaction is spontaneous

Question 5

∆Gsystem > 0

Answer 5

reaction is non-spontaneous

Question 6

∆Gsystem = 0

Answer 6

reaction is at equilibrium

Question 7

∆H = “-” and ∆S = “+”

Answer 7

always spontaneous
(∆G is always less than zero)

Question 8

∆H = “+” and ∆S = “-”

Answer 8

always non-spontaneous
(∆G is always greater than zero)

Question 9

∆H = “-” and ∆S = “-”

Answer 9

sometimes spontaneous, (∆G is negative at lower
temperatures)

T<∆H/∆S (lower temperatures)

Question 10

∆H = “+” and ∆S = “+”

Answer 10

sometimes spontaneous(∆G is negative at higher
temperatures)

T>∆H/∆S (higher temperatures)