The reaction for the complete combustion of acetylene is shown below.
C2H2(g) + 5/2 O2(g) -----------> 2 CO2(g) + H2O(l) ΔH = -1299 kJ
Use this reaction and the data below to calculate the heat of formation for acetylene.
ΔHf[H2O(l)] = -285.8 kJ/mol
ΔHf[CO2(g)] = -393.5 kJ/mol
To calculate the heat of formation for acetylene (C2H2), we need to use the heat of formation values for water (H2O) and carbon dioxide (CO2), along with the given reaction equation and the heat of combustion of acetylene.
First, let's write the balanced equation for the combustion of acetylene:
C2H2(g) + 5/2 O2(g) → 2 CO2(g) + H2O(l)
Now, we need to analyze the equation and determine the heat of formation for acetylene. By examining the coefficients in the balanced equation, we can see that the stoichiometric ratio between acetylene and water is 1:1, and the stoichiometric ratio between acetylene and carbon dioxide is 1:2.
Since we know the heat of formation values for water and carbon dioxide, we can set up an equation using the given data:
ΔH = (2 * ΔHf[CO2]) + (ΔHf[H2O]) - ΔHcombustion
Substituting the given values:
ΔH = (2 * -393.5 kJ/mol) + (-285.8 kJ/mol) - (-1299 kJ/mol)
Simplifying the equation:
ΔH = -787 kJ/mol + (-285.8 kJ/mol) + 1299 kJ/mol
This simplifies to:
ΔH = 226.2 kJ/mol
Therefore, the heat of formation for acetylene (C2H2) is 226.2 kJ/mol.