Find the enthalpy of S−S bond from the following data (only magnitude in nearest integer in kJ/mol):
(i)C2H5−S−C2H5(g)ΔHof=−147.2kJ/mol
(ii)C2H5−S−S−C2H5(g)ΔHof=−201.9kJ/mol
(iii)S(g)ΔHof=222.8kJ/mol
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Solution
C2H5−S−C2H5(g)+S(g)→C2H5−S−S−C2H5(g);ΔH
The above reaction involves 1. Breaking S-C bond (x amount of energy absorbed) 2.Making S-S bond (y amount of energy released) 3. Making S-C bond (x amount of energy released) Hence enthaply of the reaction =x-y-x = -y And -y is nothing but the enthaply of S−S bond Therefore Enthaply of S−S bond =ΔH=ΣΔHof,products−ΣΔHof,reactants=−201.9+147.2+222.8=168.1kJ/mol = 168kJ \mol