Question

identify the exothermic processes. check all that apply.
mg(s) + 2h₂o(l) → mg(oh)₂(s) + h₂(g), δh = -84.3 kcal
2cu₂o(s) → 2cu(s) + o₂(g), δh = +337.2 kj
h₂(g) + i₂(s) → 2hi(g), δh = +53. kj
n₂o₅(g) + h₂o(l) → 2hno₃(l), δh = -18.1 kcal
6h₂o(l) + 6co₂(g) → c₆h₁₂o₆(s) + 6o₂(g), δh = +2803 kj
none of the above

Explanation:

Step1: Recall exothermic definition

Exothermic processes have \(\Delta H < 0\) (release heat).

Step2: Analyze each reaction

• \( \ce{Mg(s) + 2H2O(l) -> Mg(OH)2(s) + H2(g)} \), \(\Delta H = -84.3\) kcal: \(\Delta H < 0\), exothermic.
• \( \ce{2Cu2O(s) -> 2Cu(s) + O2(g)} \), \(\Delta H = +337.2\) kJ: \(\Delta H > 0\), endothermic.
• \( \ce{H2(g) + I2(s) -> 2HI(g)} \), \(\Delta H = +53\) kJ: \(\Delta H > 0\), endothermic.
• \( \ce{N2O5(g) + H2O(l) -> 2HNO3(l)} \), \(\Delta H = -18.1\) kcal: \(\Delta H < 0\), exothermic.
• \( \ce{6H2O(l) + 6CO2(g) -> C6H12O6(s) + 6O2(g)} \), \(\Delta H = +2803\) kJ: \(\Delta H > 0\), endothermic.

Answer:

• \( \ce{Mg(s) + 2H2O(l) -> Mg(OH)2(s) + H2(g)} \), \(\Delta H = -84.3\) kcal
• \( \ce{N2O5(g) + H2O(l) -> 2HNO3(l)} \), \(\Delta H = -18.1\) kcal