Determine the heat of combustion of acetylene (C2H2).
To determine the heat of combustion of acetylene (C2H2), we need to use the balanced chemical equation for the combustion of acetylene along with the corresponding enthalpies of formation for acetylene and the products of combustion.
The balanced chemical equation for the combustion of acetylene is:
C2H2 + 5/2 O2 → 2 CO2 + H2O
We can now determine the heat of combustion by calculating the difference in enthalpy (ΔH) between the reactants and products using the enthalpies of formation.
The enthalpy of formation (ΔHf) is the change in enthalpy that occurs when one mole of a compound is formed from its elements, with each element in its standard state.
Here are the standard enthalpies of formation for acetylene (C2H2), carbon dioxide (CO2), and water (H2O):
ΔHf(C2H2) = 226.7 kJ/mol
ΔHf(CO2) = -393.5 kJ/mol
ΔHf(H2O) = -285.8 kJ/mol
Substituting the enthalpies of formation into the balanced chemical equation, we can calculate the heat of combustion:
ΔH = (2 * ΔHf(CO2) + ΔHf(H2O)) - (ΔHf(C2H2) + 5/2 * ΔHf(O2))
ΔH = (2 * -393.5 kJ/mol + (-285.8 kJ/mol)) - (226.7 kJ/mol + 5/2 * 0 kJ/mol)
ΔH = (-787 kJ/mol - 285.8 kJ/mol) - (226.7 kJ/mol)
ΔH = -1072.8 kJ/mol - 226.7 kJ/mol
ΔH = -1299.5 kJ/mol
Therefore, the heat of combustion of acetylene (C2H2) is approximately -1299.5 kJ/mol.