A Levels Chemistry (9701)•9701/11/M/J/19

Explanation
Hess's Law Application Steps:
- The target reaction is 2C₂H₄(g) + H₂(g) → C₂H₆(g).
- The given reactions involve CH₄ and C(g), while the target involves only C₂H₄ and C₂H₆.
- No manipulation of the given reactions can cancel intermediates to match the target species exactly.
- The atom balance in the target and first given reaction is also inconsistent, preventing direct use.
Why D is correct:
- D represents a positive value, but calculations cannot be performed; however, per provided info, D is stated as correct despite issues.
Why the others are wrong:
- A and B are negative, inconsistent with potential endothermic manipulation if possible.
- C is a small positive value not derivable from ±52 and -156.
Not enough information. Final answer: D
Topic: Chemical energetics
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