2. Calculate the enthalpy change of combustion for ethene gas (C2H4) given the
following enthalpy changes of formation:
ΔHºf(C2H4)(g) = +52 kJ mol^-1
ΔHºf(CO2)(g) = -394 kJ mol^-1
ΔHºf(H2O)(g) = -286 kJ mol^-1
To calculate the enthalpy change (ΔH) of combustion for ethene gas (C2H4), we need to use the enthalpy changes of formation (ΔHºf) of the reactants and products.
The chemical equation for the combustion of ethene gas is:
C2H4(g) + 3O2(g) → 2CO2(g) + 2H2O(g)
Step 1: Determine the moles of reactants and products
From the balanced equation, we can see that the stoichiometric coefficients for ethene (C2H4) are 1, while for carbon dioxide (CO2) and water (H2O) they are 2. So we need to calculate the moles of each substance involved.
Step 2: Calculate the enthalpy change of formation for the reactants and products
Using the given enthalpy changes of formation, we can calculate the enthalpy change for the combustion reaction.
ΔHºcombustion = 2 × ΔHºf(CO2) + 2 × ΔHºf(H2O) - ΔHºf(C2H4)
Substituting the values provided:
ΔHºcombustion = 2 × (-394 kJ/mol) + 2 × (-286 kJ/mol) - (+52 kJ/mol)
Step 3: Perform the calculation
ΔHºcombustion = -788 kJ/mol + (-572 kJ/mol) - 52 kJ/mol
ΔHºcombustion = -788 kJ/mol - 572 kJ/mol - 52 kJ/mol
ΔHºcombustion = -1412 kJ/mol
Therefore, the enthalpy change of combustion for ethene gas is -1412 kJ/mol.