Chemistry 5070 · O Level · Exothermic and endothermic reactions

Exothermic and endothermic reactions — practice question

The conversion of hydrogen and oxygen into liquid water can happen in three steps. 1. $2\text{H}_2(g) + \text{O}_2(g) \rightarrow 4\text{H}(g) + 2\text{O}(g)$ 2. $4\text{H}(g) + 2\text{O}(g) \rightarrow 2\text{H}_2\text{O}(g)$ 3. $2\text{H}_2\text{O}(g) \rightarrow 2\text{H}_2\text{O}(l)$ Which of these steps are exothermic?

  • A1, 2 and 3
  • B1 and 2 only
  • C2 and 3 only
  • D2 only

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