Question

Enthalpy of sublimation of graphite is 716 kJ mol^-1.

Bond enthalpy	H - H	C - H
ΔH0 kJ mol-1	436.4	414

Calculate standard enthalpy of formation of CH₄.

Answer 1

Given :

Δ_subH⁰_graphite = 716 kJ mol^-1

Bond enthalpy	H - H	C - H
ΔH0 kJ mol-1	436.4	414

Thermochemical equation for the formation of CH₄,

= [716 + 2 × 436.4] – [4 × 414] 

= [716+ 872.8] – [1656] 

= 1588.8 – 1656

= -67.2 kJ mol^-1

∴ Standard enthalpy of formation of CH₄ =