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. DH > 0, DS > 0 increase disorder, but break IMF (London forces) so endothermic

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. DH > 0, DS > 0 increase disorder, but break IMF (H bonds) so endothermic

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. DH > 0, DS > 0 increase disorder, (1 gas molecule to 2 gas molecules) but break covalent bond so endothermic

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. DH < 0, DS > 0 increase disorder (more gas molecules in products), and form more stable products so exothermic - releases lots of heat

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. DH > 0, DS < 0 decrease disorder, and make more stable bonds in product so endothermic

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. DH < 0, DS > 0 increase disorder, and exothermic

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. DH > 0, DS > 0 increase disorder but endothermic

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. DH > 0, DS > 0 increase disorder, but endothermic since break all ionic bonds

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. DH < 0, DS < 0 decrease disorder (go from gas to aq. phase), but exothermic since form many IMF (ion-water interactions)

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 since don't know if it is exothermic or endothermic