To estimate the enthalpy change (ΔH) of a reaction using average bond enthalpies, you need to calculate the energy required to break the bonds and the energy released when new bonds form.
First, let's identify the bonds in the reactants and products:
Reactants:
2 SF4 molecules: 2 (S-F) bonds
1 O2 molecule: 1 (O=O) bond
Products:
2 OSF4 molecules: 2 (O=S) bonds and 4 (S-F) bonds
Now, use the given average bond enthalpies to calculate the energy required to break the bonds:
For SF4, we have 2 (S-F) bonds:
2 × 327 kJ/mol = 654 kJ/mol
For O2, we have 1 (O=O) bond:
1 × 495 kJ/mol = 495 kJ/mol
Next, calculate the energy released when new bonds are formed:
For OSF4, we have 2 (O=S) bonds:
2 × 523 kJ/mol = 1046 kJ/mol
And we have 4 (S-F) bonds:
4 × 327 kJ/mol = 1308 kJ/mol
Now, calculate the total energy change:
Energy required to break bonds in the reactants: 654 kJ/mol + 495 kJ/mol = 1149 kJ/mol
Energy released when new bonds are formed in the products: 1046 kJ/mol + 1308 kJ/mol = 2354 kJ/mol
ΔH (rxn) = Energy of products - Energy of reactants = 2354 kJ/mol - 1149 kJ/mol = 1205 kJ/mol
Therefore, the estimated enthalpy change (ΔH) of the reaction 2SF4 + O2 → 2OSF4 is 1205 kJ/mol.