MCQ
The reaction of cyanamide, $NH _{2} CN _{( s )}$ with oxygen was run in a bomb calorimeter and $\Delta U$ was found to be $-742.24\, kJ\, mol ^{-1}$. The magnitude of $\Delta H _{298}$ for the reaction

$NH _{2} CN _{( s )}+\frac{3}{2} O _{2}( g ) \rightarrow N _{2( g )}+ O _{2}( g )+ H _{2} O _{(l)}$

is ............ $kJ$. (Rounded off to the nearest integer)

[Assume ideal gases and $\left. R =8.314\, J\, mol ^{-1} K ^{-1}\right]$

  • A
    $343$
  • $741$
  • C
    $783$
  • D
    $561$

Answer

Correct option: B.
$741$
b
$\Delta H =\Delta U +\Delta n _{ g } RT$

$=-742.24+\frac{1}{2} \times \frac{8.314}{1000} \times 298$

$=-741 kJ / mol$

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