95. Using the standard enthalpy of formation data in Appendix G, calculate the bond energy of the carbon-sulfur double bond in CS2.

+523 kJ.

Explanation:

The following data will be used to calculate the average C-S bond energy in CS2 (l).

S (s) - --> S (g)

ΔH = 223 kJ/mol

C (s) - --> C (g)

ΔH = 715 kJ/mol

Enthalpy of formation of CS2 (l)

ΔH = 88 kJ/mol

CS2 (l) - --> CS2 (g)

ΔH = 27 kJ/mol

CS2 (g) - -> C (g) + 2S (g)

So we must construct it stepwise.

1: C (s) - --> C (g) ΔH = 715 kJ

2: 2S (s) - --> 2S (g) ΔH = 446 kJ

adding 1 + 2 = 3

ΔH = 715 + 446

= 1161 kJ

3: C (s) + 2S (s) - -> C (g) + 2S (g) ΔH = 1161 kJ

4: C (s) + 2S (s) - -> CS2 (l) ΔH = 88 kJ

adding (reversed 3) from 4 = 5

ΔH = - 1161 + 88

= - 1073 kJ

5: C (g) + 2S (g) - -> CS2 (l) ΔH = - 1073 kJ

6: CS2 (l) - --> CS2 (g) ΔH = 27 kJ

adding 5 + 6 = 7

ΔH = - 1073 + 27

= - 1046 kJ

7. C (g) + 2S (g) - -> CS2 (g) ΔH = - 1046 kJ

Reverse and divide by 2 for C-S bond enthalpy

= - (-1046) / 2

= + 523 kJ.