The heat of combustion per mole for acetylene, C 2 H 2 ( g ), is -1299.5 kJ/mol.
ID: 517540 • Letter: T
Question
The heat of combustion per mole for acetylene, C2H2(g), is -1299.5 kJ/mol. Assuming that the combustion products are CO2(g) and H2O(l), and given that the enthalpy of formation is -393.5 kJ/mol for CO2(g) and -285.8 kJ/mol for H2O(l), find the enthalpy of formation of C2H2(g).
The heat of combustion per mole for acetylene, C2H2(g), is -1299.5 kJ/mol. Assuming that the combustion products are CO2(g) and H2O(l), and given that the enthalpy of formation is -393.5 kJ/mol for CO2(g) and -285.8 kJ/mol for H2O(l), find the enthalpy of formation of C2H2(g).
-846.1 kJ/mol -226.7 kJ/mol +226.7 kJ/mol -620.2 kJ/molExplanation / Answer
The reaction taking place is:
2C2H2 (g) + 5O2 (g) —> 4CO2 (g) + 2H2O (l)
In balanced reaction there are 2 mol of C2H2
so,
Ho rxn = 2*(-1299.5) = -2599 KJ
Use:
Ho rxn = 4*Hof(CO2(g)) + 2*Hof(H2O(l)) - 2*Hof( C2H2(g)) - 5*Hof(O2(g))
-2599 = 4*-393.5 + 2*-285.8 - 2*Hof( C2H2(g)) - 5*0.0
2*Hof( C2H2(g)) = 453.4
Hof( C2H2(g)) = 226.7 KJ/mol
Answer: + 226.7 KJ/mol
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