Find the bond enthalpy of S-S bond from the following data (in kJ):
$C_{2} H_{5} - S - C_{2} H_{5} (g) Δ_{f} H^{0} = - 147 k J m o l^{- 1}$
$C_{2} H_{5} - S - S - C_{2} H_{5} (g) Δ_{f} H^{0} = - 201 k J m o l^{- 1}$
$S_{(s)} \to S_{(g)} Δ_{f} H^{0} = 222 k J m o l^{- 1}$

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answer is 276.

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Detailed Solution

i) $4 C (s) + 5 H_{2} (g) + S (s) \to C_{2} H_{5} - S - C_{2} H_{5} (g) Δ_{r} H^{0} = - 147 k J m o l^{- 1}$
ii) $4 C (s) + 5 H_{2} (g) + 2 S (s) \to C_{2} H_{5} - S - S - C_{2} H_{5} (g) Δ_{r} H^{0} = - 201 k J m o l^{- 1}$
Subtracting Eq(i)from Eq.(ii), we get
$C_{2} H_{5} - S - S C_{2} H_{5} (g) + S (s) \to C_{2} H_{5} - S - S - C_{2} H_{5} (g)$
Adding to this, the following equation
$S (g) \to S (s)$
We get
$C_{2} H_{5} - S - C_{2} H_{5} (g) + S (g) \to C_{2} H_{5} - S - S - C_{2} H_{5} (g)$
In the last equation 276kJ of heat evolved because of the S-S bond formation.
Hence the bond enthalpy of S-S is $276 k J m o l^{-}$