WCB Quiz:DG, DH, and DS

For the following reactions, remember that ΔH < 0 for an exothermic reaction, ΔH > 0 for an endothermic reaction, ΔS > 0 when disorder increases, and ΔS < 0 when disorder decreases (order increases).

1. For the reaction N2(l) --> N2(g)

a. ΔH > 0, ΔS > 0

b. ΔH > 0, ΔS < 0

c. ΔH < 0, ΔS > 0

d. ΔH < 0, ΔS < 0

e. insufficient information given

2. For the reaction H2O(s) --> H2O (l)

a. ΔH > 0, ΔS > 0

b. ΔH > 0, ΔS < 0

c. ΔH < 0, ΔS > 0

d. ΔH < 0, ΔS < 0

e. insufficient information given

3. For the reaction H2(g) --> 2H (g)

a. ΔH > 0, ΔS > 0

b. ΔH > 0, ΔS < 0

c. ΔH < 0, ΔS > 0

d. ΔH < 0, ΔS < 0

e. insufficient information given

4. For the reaction 2C6H14(l) + 19O2(g) --> 12CO2(g) + 14H2O (g)

a. ΔH > 0, ΔS > 0

b. ΔH > 0, ΔS < 0

c. ΔH < 0, ΔS > 0

d. ΔH < 0, ΔS < 0

e. insufficient information given

5. For the reaction 6CO2(g) + 6H2O(l) --> 6C6H12O6 (s) + O2(g)

a. ΔH > 0, ΔS > 0

b. ΔH > 0, ΔS < 0

c. ΔH < 0, ΔS > 0

d. ΔH < 0, ΔS < 0

e. insufficient information given

When certain salts dissolve in water, the solution warms, but when other salts dissolve, the solution cools.

6. When MgCl2(s) dissolves in water, the solution warms. For the reaction MgCl2(s) --> MgCl2(aq)

a. ΔH > 0, ΔS > 0

b. ΔH > 0, ΔS < 0

c. ΔH < 0, ΔS > 0

d. ΔH < 0, ΔS < 0

e. insufficient information given

7. When K2SO4(s) dissolves in water, the solution cools. For the reaction K2SO4(s) -->K2SO4(aq)

a. ΔH > 0, ΔS > 0

b. ΔH > 0, ΔS < 0

c. ΔH < 0, ΔS > 0

d. ΔH < 0, ΔS < 0

e. insufficient information given

The reaction MgCl2(s) --> MgCl2(aq) described in question 6, can be throught of as occuring in two very hypothetical steps.

STEP 1: MgCl2(s) --> Mg2+(g) + 2Cl-(g).

STEP 2: Mg2+(g) + 2Cl-(g) --> Mg2+(aq) + 2Cl-(aq)

8. For STEP 1

a. ΔH > 0, ΔS > 0

b. ΔH > 0, ΔS < 0

c. ΔH < 0, ΔS > 0

d. ΔH < 0, ΔS < 0

e. insufficient information given

9. For STEP 2

a. ΔH > 0, ΔS > 0

b. ΔH > 0, ΔS < 0

c. ΔH < 0, ΔS > 0

d. ΔH < 0, ΔS < 0

e. insufficient information given

10. For the reaction NaF(s) + H2O(l) --> NaF(aq)

a. ΔH > 0, ΔS > 0

b. ΔH > 0, ΔS < 0

c. ΔH < 0, ΔS > 0

d. ΔH < 0, ΔS < 0

e. insufficient information given