Answer to Question #100126 in General Chemistry for Beverlie

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 $182.5\ kJ/mol$