In solid ammonia, each `NH_(3)` molecule has six other `NH_(3)` molecules as nearest neighbours. `DeltaH` sublimation of `NH_(3)` at the melting point is `30.8 k J mol^(-1)`, and the estimated `DeltaH` sublimation in the absence of hydrogen bonding is `14.4 kJ mol^(-1)`. the strength of a hydrogen bond is `NH_(3)` is

Options

A. `5.5 kJ mol^(-1)`
B. `98.4 kJ mol^(-1)`
C. `2.73 kJ mol^(-1)`
D. `8.2 kJ mol^(-1)`

Explanation

Total strength of all `H-` bonds
`=30.8-14.4 =16.4 kJ mol^(-1)`
There are `6` nearest neighbours, but each H-bonds involves only two molecules. Thus total `H`-bonds `=6/2=3`
`:. ` Strength of `H`-bond `16.4/3=5.5 k J mol^(-1)`