Question

The table below shows some values for standard enthalpy changes of combustion.



Substance

incrementHc Ө / kJ mol−1

C(s)

−394

H2(g)

−286

CH4(g)

−890



Use these values in the table above to calculate the standard enthalpy change of the reaction

C(s) + 2H2(g) ® CH4(g)


-210 kJ


-604 kJ


-76 kJ


-318 kJ

Answer 1

The correct calculation is:

ΔH = ΔHf (products) - ΔHf (reactants)
ΔH = [(-890 kJ/mol) - (2*(-286 kJ/mol))] - (-394 kJ/mol)
ΔH = (-890 kJ/mol + 572 kJ/mol) - (-394 kJ/mol)
ΔH = -318 kJ/mol

Therefore, the standard enthalpy change of the reaction C(s) + 2H2(g) ® CH4(g) is -318 kJ. The option closest to this value is -318 kJ.