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Bond dissociation enthalpies of H(2(g)) ...

Bond dissociation enthalpies of `H_(2(g)) and N_(2(g))` are `"426.0 kJ mol"^(-1)` and `"941.8 kJ mol"^(-1)`, respectively, and enthalpy of formation of `NH_(3(g))" is "-"46 kJ mol"^(-1)`. What are the enthalpy of atomisation of `NH_(3(g))` and the average bond enthalpy of `N-H` bond respectively ( in kJ `"mol"^(-1)`)?

A

1170.9, 390.3

B

117, 300

C

300, 200

D

2000, 1975

Text Solution

Verified by Experts

The correct Answer is:
A
`N_(2(g))+3H_(2(g))rarr 2NH_(3(g)), Delta H=-2xx"46 kJ mol"^(-1)`
`DeltaH=Sigma(BE)_("reactants")-Sigma(BE)_("products")`
`=(941.8+3xx436)-(6x)=-2xx46`
(here `x=BE" or "N-H" bonds")`
`x = 390.3" kJ mol"^(-1)`
`NH_(3) rarr N+3(H)`
`"Heat of atomisation "=3xx 390.3=1170.9" kJ mol"^(-1)`
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