find the entahalpy of the S-S bond from the following data

1 c₂h₅-S-S-C₂H₅(g) delta H_f= -147.2kJ/mol

2 C₂H₅-S-S-C₂H₅(g) delta H_f= -201.9kJ/mol

3 S(g) delta H_f =+222.8kJ/mol

Solution: 4C (s) + 5H2 (s) + S(s) → C2H5-S-C2H5 (g) ΔHºf= -147.23 kJ/mol --------- (1) 4C (s) + 5H2 (s) + 2S(s) → C2H5-S-S-C2H5 (g) ΔHºf= -201.92 kJ/mol --------- (2) S(g) → S (s) ΔHºf= -222.80 kJ/mol Reversing equation 1 and adding this to 2 and 3, C2H5-S-C2H5 (g) + S (g) → C2H5-S-S-C2H5 (g) ΔHºf= -277.49 kJ/mol -277.49 kJ is the heat evolved due to the formation of S-S bond. Therefore, the bond enthalpy of S-S bond is 277.49 kJ/mol.