Which of the following processes is endothermic, given the following:S(s) + O2(g) →SO2(g) ΔH = –299 kJ/molS(s) + 3/2 O2(g) →SO3(g) ΔH
Answer
Identifying the Endothermic Process
Given thermochemical data:
Equation 1: S(s) + O2(g) → SO2(g) ΔH = –299 kJ/mol
Equation 2: S(s) + 3/2 O2(g) → SO3(g) ΔH = –395 kJ/mol
We are to identify which of the following is endothermic:
- (1/2) S(s) + (1/2) O2(g) → (1/2) SO2(g)
- SO3(g) → S(s) + (3/2) O2(g)
- 2 S(s) + 2 O2(g) → 2 SO2(g)
- 2 S(s) + (5/2) O2(g) → SO2(g) + SO3(g)
- 2 S(s) + 3 O2(g) → 2 SO3(g)
🔍 Analysis:
- The reverse of an exothermic reaction is always endothermic.
- From Equation 2:
- S(s) + (3/2) O2(g) → SO3(g) ΔH = –395 kJ/mol
- SO3(g) → S(s) + (3/2) O2(g) ΔH = +395 kJ/mol
✅ Correct Answer: SO3(g) → S(s) + (3/2) O2(g) is the only endothermic process among the given options.
Explanation: This reaction absorbs energy from its surroundings to break down SO3 into elemental sulfur and oxygen — characteristic of an endothermic process.