The enthalpy of combustion for H2, C (graphite) and CH4 are -285.8, -393.5, and -890.4 kJ/mol respectively. Calculate the standard enthalpy of formation ∆Hf for CH4.

Asked by Topperlearning User | 15th Jun, 2016, 05:36: PM

Expert Answer:

We can write equation as,
C + 2H2 → CH4
Enthalpy of formation.
(1) H2(g) + 0.5 O2(g) → H2O(l)                    Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '. = -285.8 (kJ/mol)
(2) C(graphite) + O2(g) → CO2(g)                 Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '. = -293.5  (kJ/mol)
 
Enthalpy of combustion methane
(3) CH4(g) + 2O2(g) →CO2(g) + 2H2O(l)       Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '.  = -890.4(kJ/mol)

Step1. Multiply equation 1 by 2
(1) H2(g) + 0.5 O2(g) → H2O(l)                    Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '. = -285.8 (kJ/mol) x 2
 
(4) 2H2(g) + O2(g) → 2H2O(l)                      Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '. = -571.6 (kJ/mol)
Step2. To 4 add 2 and subtract 3

Syntax error from line 1 column 49 to line 1 column 73. Unexpected '<mstyle '. = 2 x (-285.8) + (-393.5) - (-890.4) = -74.7 (kJ/mol)

Answered by  | 15th Jun, 2016, 07:36: PM