Question

The gasification of coal is a method of producing methane by the following reaction. C(s) + 2H2(g) → CH4(g) ∆H=?

Find ∆H by using the enthalpy changes in the following combustion reactions:
C(s) + O2(g) → CO2(g) ∆H=-394 kj
H2(s) + ½ O2(g) → H2O(l) ∆H=-286kj
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) ∆H=-891kj

(A) 75 kJ
(B) -75 kJ
(C) 1856 kJ
(D) -1856 kJ

Answer 1

Hello there.

The gasification of coal is a method of producing methane by the following reaction. C(s) + 2H2(g) → CH4(g) ∆H=?
Find ∆H by using the enthalpy changes in the following combustion reactions:
C(s) + O2(g) → CO2(g) ∆H=-394 kj
H2(s) + ½ O2(g) → H2O(l) ∆H=-286kj
CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) ∆H=-891kj

(B) -75 kJ

Answer 2

Using Hess' Law, we can calculate the heat of reaction of the gasification of coal. Multiplying the second reaction by 2 and reversing the third reaction:

C(s) + O2(g) → CO2(g) ∆H=-394 kj
2H2(s) + O2(g) → H2O(l) ∆H=-572kj
CO2(g) + 2H2O(l) → CH4(g) + 2O2(g) ∆H=891kj

Adding the three reaction would result to
C(s) + 2H2(g) → CH4(g) ∆H = -394 + -572 + 891 = -75 kJ

The answer is
(B) -75 kJ