1.

The heats of atomisation of PH_(3)(g) and P_(2)H_(4)(g) are 954 kJ mol^(-1) and 1485 kJ mol^(-1) respectively. The P-P bond energy in kJ mol^(-1) is

Answer»

213
426
318
1272

Solution :`PH_(3) (g) RARR P (g) + 3H (g), DELTA H^(@) = 954 kJ mol^(-1)`
The bond energy is average energy for 3 P - H bonds as :
Average bond energy of P - H bond `= (954)/(3)`
`= 318 kJ mol^(-1)`
`P_(2)H_(4)` has four P - H bonds and one P - P bond
`B. E. (P - P) + 4 B. E. (P - H) = 1485 kJ mol^(-1)`
`B. E. (P - P) + 4 xx 318 = 1485 kJ mol^(-1)`
`B. E. (P - P) = 1485 - 4 xx 318`
`= 1485 - 1272 = 213 kJ mol^(-1)`


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