question_answer 1)

  Consider the reactions given below. On the basis of these reactions find out which of the algebraic relations given in options (a) to (d) is correct? (i) \[C(g)+4H(g)\to C{{H}_{4}}(g);\]\[{{\Delta }_{r}}H=x\,kJ\,mo{{l}^{-1}}\] (ii) \[C(graphite)+2{{H}_{2}}(g)\to C{{H}_{4}}(g);\]\[{{\Delta }_{r}}H=y\,kJ\,mo{{l}^{-1}}\]                 (a) \[x=y\]                           (b) \[x=2y\]                        (c) \[x>y\]                           (d) \[x<y\]                

Answer:

  (c)\[\Delta H\] (Heat of reaction) = \[\Sigma \] Bond energy of reactants \[-\Sigma \] Bond energy of products Bond energy of products are same in both reactions but bond energy of reactants are different. In second reaction, some energy is used to decompose the bonds of the molecule.