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Consider the following data : Delta(f)H^...

Consider the following data : `Delta_(f)H^(@)(N_(2)H_(4),l)=50kJ//mol,Delta_(f)H^(@)(NH_(3),g)=-46kJ//mol`
`B.E(N-H)=393" kJ//mol and B.E."(H-H)=436kJ//mol`
`Delta_("vap")H(N_(2)H_(4),l)=18kJ//mol`
The N-N bond energy in `N_(2)H_(4)` is :

A

226 kJ/mol

B

154 kJ/mol

C

190 kJ/mol

D

None of these

Text Solution

Verified by Experts

The correct Answer is:
C
`(1)/(2)N_(2)(g)+(3)/(2)H_(2)(g)rarrNH_(3)(g)`
Let B.E. of `N-=N` is x
`-46 = (x)/(2)+(3)/(2)xx436 - 3xx393 implies x = 958`
`N_(2)H_(4)(l) rarrN_(2)(g)+2H_(2)(g),`
`Delta_(r )H=-50 " kJ"//"mol"`
`Delta_(r)H=[(Delta_("vap")H(N_(2)H_(4),l)),(+4xxB.E.(N-H)),(+B.E.(N-N))]`
`-((B.E.(N-=N)),(+2B.E.(H-H)))`
`-50 =(18+4xx393+y)-(958 + 2xx436)`
`-50=(1590+y)-(1830)`
`B.E. (N-N) or y = 190 kJ/mol
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