Question

Calculate the enthalpy of hydrogenation of C₂H_4(g), given that the enthalpy of formation of ethane and ethylene are −30.2 kcal and +12.5 kcal respectively.

Options

• −4.8 kcal

• +7.7 kcal

• −42.7 kcal

• −7.7 kcal

Answer 1

−42.7 kcal

Explanation:

Given that,

\[\ce{2C_{(s)} + 3H2_{(g)} -> C2H6_{(g)}}\]; ΔH = −30.2 kcal .........(i)

\[\ce{2C_{(s)} + 2H2_{(g)} -> C2H4_{(g)}}\]; ΔH = +12.5 kcal .....(ii)

Subtracting eq. (ii) from (i), we get

\[\ce{C2H4_{(g)} + H2_{(g)} -> C2H6_{(g)}}\]; ΔH = −42.7 kcal