Answer to Question #157256 in General Chemistry for Sean

Question

Calculate the ΔHo for methane gas , CH4, produced from graphite and hydrogen gas according

to the following reaction: C(graphite) + 2H2(g)  CH4(g)

Data given:

a. C(graphite) + O2(g)  CO2(g) ΔHo= -393.5 kJ

b. H2(g) + ½ O2(g)  H2O(l) ΔHo= - 285.8 kJ

c. CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) ΔHo = -890.4kJ

Answer 1

Solution:

Data given:         

a) C(graphite) + O₂(g)                   CO₂(g)                        ΔH^o= -393.5 kJ…….  (i)

b) H₂(g) + ½ O₂(g)                   H₂O(l)                               ΔH^o= - 285.8 kJ……… (ii)

 c) CH₄(g) + 2O₂(g)               CO₂(g) + 2H₂O(l)                ΔH^o = -890.4kJ ……….(iii)

(i) + 2 x (ii) – (iii) gives

C(graphite) + 2 H₂(g)              CH₄(g)

After such rearrangement

The value of ΔH^o is = [(-393.5) + 2 x(- 285.8) + 890.4] kJ = -74.7 kJ (Ans)