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Given (A) 2CO (g) + O2 (g) → 2CO2 (g) ΔH°1 = −x kJ mol−1 (B) C(graphite) + O2 (g) → CO2 (g) ΔH°2 = −y kJ mol−1 The ΔH° for the reaction C(graphite) + 1/2 O2 (g) → CO (g) is
- (2x − y)/2
- (x + 2y)/2
- (x − 2y)/2
- 2y − x
Correct answer: (x − 2y)/2
Solution
The correct option is derived from Hess's law, which states that the total enthalpy change for a reaction is the sum of the enthalpy changes for individual steps. By manipulating the given reactions (A) and (B) to match the desired reaction, we can calculate the enthalpy change as (x - 2y)/2.
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