The standard heats of formation of `NO_(2)(g)` and `N_(2)O_(4)(g)` are 8.0 and 2.0 Kcal `mol^(-1)` respectively the heat of dimerization of `NO_(2)` in Kcal is

Options

A. `10.0`
B. `- 6.0 `
C. ` + 14.0`
D. `- 14.0`

Answer

D

Explanation

`(1)/(2) N_(2)+O_(2) rarr NO_(2), DeltaH = 8 kcal` ...(i)
`N_(2)+ 2O_(2) rarr N_(2)O_(4), DeltaH=2kcal` ....(ii)
Aim `: 2NO_(2) rarrN_(2)O_(4) , DeltaH=?`
Eqn. (ii) `- 2 xx `Eqn. (i) gives
`0= N_92)O_94) - 2NO_(2)`or `2NO_(2) rarr N_(2)O_(4), DeltaH= 2-2(8) = -14.0 kcal`