Question

7. Using Hess’ Law, what is the enthalpy of reaction, ΔH, for the formation of methane, CH4, from solid carbon and hydrogen gas?

C(s) + 2 H2(g) = CH4(g)

Use the following reactions to determine the answer:

H2(g) + 1/2 O2(g) = H2O(l) ΔHo = -393.5 KJ

C(s) + O2(g) = CO2(g) ΔHo = -285.8 KJ

CH4(g) + O2(g) = CO2(g) + H2O (l) ΔHo= -890.3 KJ

Answer 1

$$H_2+\frac{1}{2}O_2\to H_2O\ .....(1)\ -393.5kJ$$

$$C+O_2\to CO_2\ ....(2)\ -285.8\ kJ$$

$$2H_2O+ CO_2\to CH_4+ 2O_2 \ ....(3)\ 890.3\ kJ$$

$$Applying\ (2)\ +(2\times(1))\ +(3)$$

$$C+2H_2\to CH_4\ ....(4)\ -182.5\ kJ/mol$$

Hence enthaly of formation of methane is $182.5\ kJ/mol$