The difference in the heat of formation of ammonia at constant pressure and that at a constant volume at $300$ K is: (R $= 8.314 J K^{- 1} m o l^{- 1}$ ).

2.494

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- 2.494

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3.944

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- 3.944

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Solution

The correct option is B $- 2.494$ kJ
$△ H = △ U + △ n R T$
Where $△$ H is a heat of formation at Constant Pressure
$△$ U is a heat of formation at constant volume
R is universal gas constant
$△$ n = number of moles of gas on product side - a number of moles of gas on reactant side.
Reaction : $\frac{1}{2}$ $N_{2}$ + $\frac{3}{2}$ $H_{2}$ $\to$ N $H_{3}$
So $△ n$ = -1

So , $△ H$ - $△ U$ = $△ n$ RT
Hence $△ H$ - $△$ U= -1 $\times$ 8.314 $\times$ 300 $= - 2494.2 J$ or $- 2.494 k J$

Option B is correct

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The difference in the heat of formation of ammonia at constant pressure and that at a constant volume at 300K is: (R=8.314JK−1mol−1).

The difference in the heat of formation of ammonia at constant pressure and that at a constant volume at $300$ K is: (R $= 8.314 J K^{- 1} m o l^{- 1}$ ).