Given ΔHc of C(s) = −393.5, H₂(g) = −285.8 and CH₄(g) = −890.3 kJ mol⁻¹, what is the standard enthalpy of formation of methane?
Correct answer D. −74.8 kJ mol⁻¹
Explanation
By Hess's law, ΔHf(CH₄) = ΔHc(C) + 2ΔHc(H₂) − ΔHc(CH₄) = −393.5 − 571.6 + 890.3 = −74.8 kJ mol⁻¹.
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