Question

On the basis of following equations the heat of dimerisation of `NO_(2)` will be
(i) `N_(2)+2O_(2)rarr2NO_(2) " "DeltaH=67.9 kJ`
(ii) `N_(2)+2O_(2)rarrN_(2)O_(4) " "DeltaH=09.3 kJ`
A. `+77.2 kJ`
B. `-77.2 kJ`
C. `-58.6 kJ`
D. `+58.6 kJ`

Answer 1

Correct Answer - C
Our desirable equation is
`2NO_(2)rarrN_(2)O_(4)" ...(iii)"`
Given
`2NO_(2)rarrN_(2)+2O_(2)DeltaH=-67.9 kJ " ...(i)"`
`N_(2)O_(4)rarrN_(2)+2O_(2)DeltaH=-09.3 kJ " ...(ii)"`
On substracting equation (ii) from (i) we will get equation (iii)
`2NO_(2)-N_(2)O_(4)rarr0`
`2NO_(2)rarrN_(2)O_(4)" ....(iii)"`
So Heat of dimerisation of `NO_(2)=-67.9-(-09.3)kJ=-67.9+9.3 =-58.6 kJ`