The enthalpy of combustion of acetylene C₂H₂ is described by C₂H₂(g) + (5/2) O₂(g) $\rarr$ 2CO₂(g) + H₂O(l) , $\Delta$ H^$\circ$_rxn= -1299 kJ/mol.Calculate the enthalpy of formation of acetylene, given the following enthalpies of formation
$\Delta$ H^$\circ$_f[CO₂(g) ] = -393.5 kJ/mol
$\Delta$ H^$\circ$_f[H₂O(l) ] = -285.8 kJ/mol

Question

The enthalpy of combustion of acetylene C₂H₂ is described by C₂H₂(g) + (5/2) O₂(g)

\rarr

2CO₂(g) + H₂O(l) ,

\Delta

H^$\circ$_rxn= -1299 kJ/mol.Calculate the enthalpy of formation of acetylene, given the following enthalpies of formation

\Delta

H^$\circ$_f[CO₂(g) ] = -393.5 kJ/mol

\Delta

H^$\circ$_f[H₂O(l) ] = -285.8 kJ/mol

Quizplus · Accepted Answer

The enthalpy of formation of acetylene can be calculated using the enthalpy of combustion and the enthalpies of formation of the reactants and products involved in the reaction:

ΔH°f(C2H2) = [2ΔH°f(CO) + ΔH°f(H2O)] - ΔH°comb

Substituting the given values:

ΔH°f(C2H2) = [2(-393.5 kJ/mol) + (-285.8 kJ/mol)] - (-1299 kJ/mol)
ΔH°f(C2H2) = -226 kJ/mol

Note that the enthalpy of formation is usually given as a positive value, but in this case, it is negative because the reaction is exothermic. Therefore, the closest answer choice is B, which is 226 kJ/mol.

The Enthalpy of Combustion of Acetylene C2H2 Is Described by C2H2(g)

The Enthalpy of Combustion of Acetylene C₂H₂ Is Described by C₂H₂(g)