Question

1. consider this equation and its heat of reaction.

2c₄h₁₀(g) + 13o₂(g) → 8co₂(g) + 10h₂o(g) δh = -5320 kj
an alternate way to express the same information is:
a. c₄h₁₀(g) + 13/2 o₂(g) → 4co₂(g) + 5h₂o(g) + 5320 kj
b. 2c₄h₁₀(g) + 13o₂(g) + 5320 kj → 8co₂(g) + 10h₂o(g)
c. 8co₂(g) + 10h₂o(g) → 2c₄h₁₀(g) + 13o₂(g) + 5320 kj
d. 8co₂(g) + 10h₂o(g) → 2c₄h₁₀(g) + 13o₂(g) - 5320 kj

1. a correct interpretation of an exothermic reaction is that during the reaction the:

a. surroundings gain energy
b. surroundings lose energy
c. reactants gain energy to form products
d. heat of the products is greater than heat of the reactants

1. which of the below reactions are exothermic?

i c(s) + h₂(g) → ch₄(g) δh = +226.7 kj
ii ½n₂(g) + ½o₂(g) → no(g) δh = +90.3 kj
iii 4c(s) + 5h₂(g) → c₄h₁₀(g) δh = -124.7 kj
iv mg(s) + ½o₂(g) → mgo(s) δh = -601.8 kj
a. i and ii
b. i and iii
c. ii and iii
d. iii and iv

1. which of the following reactions is endothermic?

a. h₂(g) + ½o₂(g) → h₂o(l) δh = -242.76 kj
b. ch₄(g) + 2o₂(g) → 2co₂(g) + 4h₂o(g) δh = -2059.6 kj
c. al(s) + 3fe²⁺(aq) → al³⁺(aq) + 3fe(s) δh = -1306.2 kj
d. h₂o(g) + c(s) → co(g) + h₂(g) δh = 131.88 kj

1. which of the following is an endothermic change?

a. hot coffee cooling to room temperature
b. steam condensing to water on a cold window.
c. frost forming on a windshield
d. ice melting

Explanation:

Question 3

Exothermic reactions have negative \(\Delta H\), meaning energy is released. Option b adds energy as a reactant, which is incorrect. Wait, no—wait, the original reaction is exothermic (\(\Delta H=-5320\text{ kJ}\)), so energy is a product. Option b has energy on the reactant side, which is wrong. Wait, no, the options: let's check again. Original: \(2\text{C}_4\text{H}_{10}(g)+13\text{O}_2(g)
ightarrow8\text{CO}_2(g)+10\text{H}_2\text{O}(l)\) \(\Delta H=-5320\text{ kJ}\). Exothermic: energy released (product). So alternative expression is to write energy as product: \(2\text{C}_4\text{H}_{10}(g)+13\text{O}_2(g)
ightarrow8\text{CO}_2(g)+10\text{H}_2\text{O}(l)+5320\text{ kJ}\), which is option b? Wait the options: a. \(2\text{C}_4\text{H}_{10}(g)+13\text{O}_2(g)+5320\text{ kJ}
ightarrow...\) (reactant side: endothermic). b. \(2\text{C}_4\text{H}_{10}(g)+13\text{O}_2(g)
ightarrow...+5320\text{ kJ}\) (product side: correct for exothermic). Yes, so answer b.

Question 4

Exothermic reaction: system releases energy, surroundings gain energy. So answer A.

Question 5

Endothermic: \(\Delta H>0\). Reaction I: \(\Delta H=+226.7\text{ kJ}\) (endothermic). Reaction II: \(\Delta H=-1742\text{ kJ}\) (exothermic). Reaction III: \(\Delta H=+172.4\text{ kJ}\) (endothermic). Reaction IV: \(\Delta H=-601.8\text{ kJ}\) (exothermic). So I and III are endothermic. Answer b.

Question 6

Endothermic: \(\Delta H>0\). Option d has \(\Delta H=131.88\text{ kJ}\) (positive). Answer d.

Question 7

Endothermic change: absorbs heat. Ice melting requires heat (endothermic). Others: cooling (releases), condensing (releases), frost forming (freezing, releases). Answer d.

Answer:

1. b. \(2\text{C}_4\text{H}_{10}(g) + 13\text{O}_2(g) + 5320\text{ kJ}

ightarrow 8\text{CO}_2(g) + 10\text{H}_2\text{O}(l)\)

1. A. Surroundings gain energy
2. c. II and III
3. d. \(\text{H}_2\text{O}(l) + \text{C}(s)

ightarrow \text{CO}(g) + \text{H}_2(g)\) \(\Delta H = 131.88\text{ kJ}\)

1. d. Ice melting