The standard heats of formation of NO $_{2}$ (g) and N $_{2}$ O $_{4}$ (g) are 33.5 and 8.4 KJ mol $^{- 1}$ respectively.
The heat of dimerisation of NO $_{2}$ in KJ is:

Q. The standard heats of formation of

N O_{2}

(g) and

N_{2} O_{4}

(g) are

8.0

and

2.0 k c a l m o l^{- 1}

respectively, the heat of dimerization of

N O_{2}

k c a l

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The standard heats of formation in K.cal mol −1 of NO2(g) and N2O4(g)are 8.0 and 2.0 respectively. The heat of dimerisation of NO2 in K.cal is 2NO2(g)→N2O4(g)

The correct option is D -142NO2(g)→N2O4(g)Heat of dimerisation =ΔHp−ΔHR =2−8×2= - 14 Kcal Mol−1Option D is correct.

The standard heats of formation in K.cal mol $^{- 1}$ of NO $_{2 (g)}$ and N $_{2}$ O $_{4 (g)}$ are 8.0 and 2.0 respectively. The heat of dimerisation of $N O_{2}$ in K.cal is $2 N O_{2 (g)} \to N_{2} O_{4 (g)}$

The correct option is D -14
$2 N O_{2} (g) \to N_{2} O_{4} (g)$
Heat of dimerisation $= Δ H_{p} - Δ H_{R}$ = $2 - 8 \times 2$
$=$ - 14 Kcal Mol $^{- 1}$

Option D is correct.