question_answer 58)

  The value of\[{{\Delta }_{f}}{{H}^{{}^\circ }}\]for \[N{{H}_{3}}\] is\[-9.18kJmo{{l}^{-1}}\]. Calculate enthalpy change for the following reaction: \[2N{{H}_{3}}(g)\to {{N}_{2}}(g)+3{{H}_{2}}(g)\]                

Answer:

  The given reaction: \[2N{{H}_{3}}(g)\to {{N}_{2}}(g)+2{{H}_{2}}(g)\] \[{{\Delta }_{r}}{{H}^{{}^\circ }}=[{{\Delta }_{f}}H_{{{N}_{2}}}^{{}^\circ }+3{{\Delta }_{f}}H_{{{H}_{2}}}^{{}^\circ }]-[2{{\Delta }_{f}}H_{N{{H}_{3}}}^{{}^\circ }]\]\[=0+3\times 0-2\times (-91.8)\] \[=+183.6kJ\]