Question

N2+3H2 -- 2NH3
calculate enthalpy change if bond enthalpy for
N -N =946
H-H=435
N-N=389

Answer 1

The Enthalpy Change during the reaction

N2+3H2 -- 2NH3   is   41.5 KJ/mol

• The Enthalpy change or Heat of reaction- It is the amount of heat released or absorbed by the reactants, to form 1 mole of product , at constant pressure.
• Bond Enthalpy- The amount of heat stored in between atoms of a molecule.
• It is the amount of energy required to break the bond between the atoms of that molecule.
• The Enthalpy change of a reaction = (Sum of Bond enthalpies of products) - (Sum of bond enthapies of reactants)
• For reaction, 1/2 N2+3/2 H2 -- NH3                                                                          {3 (389) - [1/2 (946) + 3/2 (435) ] } KJ/mol =1167 - 473 - 652.5 = 41.5 KJ/mol