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NEET levelSingle correct optionDifficulty 1 of 3td113

For which of the following reactions at constant temperature is $Δ H = Δ U$ ?

A $N X_{2} (g) + 3 H X_{2} (g) 2 NH X_{3} (g)$
B $PCl X_{5} (g) PCl X_{3} (g) + Cl X_{2} (g)$
C $2 SO X_{2} (g) + O X_{2} (g) 2 SO X_{3} (g)$
D $H X_{2} (g) + I X_{2} (g) 2 HI (g)$

Answer: D

Δ H = Δ U + Δ n_{g} RT

. The two are equal only when

Δ n_{g} = 0

. For

H X_{2} + I X_{2} 2 HI

,

Δ n_{g} = 2 - 2 = 0

; the other three have

Δ n_{g} = - 2, + 1, - 1

respectively.

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