If heat contents of CH4, C2H4 and C3H8 are -17.9, 12.5 and -24.8 kcal/mole respectively, than ΔH for the reaction CH4(g) + C2H4(g) ⇋ C3H8(g) will be __________ Kcal.

Answer: Option A

Since the enthalpy change $$=$$ enthalpy or heat content of the products $$–$$ enthalpy or heat content of the reactants $$=-24.8+17.9-12.5=-\mathrm{19.4.}$$