13. Given N₂(g) + 3H₂(g) → 2NH₃(g); ?_r H^– = -92.4 kJ mol^-1. What is the standard enthalpy of formation of NH₃ gas? 

 

<p><strong>13.&nbsp;</strong>N₂&nbsp; (g) + 3H₂&nbsp; (g) → 2NH₃&nbsp; (g);&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;? _rH= -92.4 kJ/mol&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</p><p>Standard enthalpy of formation of a compound is the change in enthalpy that takes place during the formation of a substance in its standard form from its constituent elements in their standard state.</p><p>Re-writing the given equation for 1 mol of NH₃</p><p>1/2N₂&nbsp; (g) + 3/2H₂&nbsp; (g) → NH₃&nbsp; (g);</p><p>Standard enthalpy of formation of NH₃= ½? rH</p><p>? _fH (g) = – (92.4)/2 = – 46.2 kJ mol^-1</p>

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