The standard heat of formation values of `SF_(6)(g), S(g)`, and `F(g)` are `-1100, 275`, and `80 kJ mol^(-1)`, respectively. Then the average `S-F` bond enegry in `SF_(6)`

Answer

`309.16 kJ mol^(-1)`

Explanation

Given : `SF_(6) (g) rarr S (g) + 6 F (g) , Delta H = ?`
From the available data, we can write the following equation
(i) `S (s) + 3F_(2) (g) rarr SF_(6) , Delta H = - 1100.0 kJ`
(ii) `S (s) rarr S (g) , Delta H = 275.0 kJ`
(iii) `(1)/(2) F_(2) (g) rarr F(g) , Delta H = 80.0 kJ`
To get the required equation carry out the following computation `[6 xx (iii) + (ii)] - (i)`
i.e. `Delta H = (6 xx 80 + 2745) - (- 1100.0) = 1855 kJ`
Now, in `SF_(6)` we find `S - F` bonds, therefore the bond energy. Thus average bond energy for `S - F` bond `= (1855)/(6) = 309.16 kJ mol^(-1)`