question_answer

For an endothermic reaction, energy of activation is \[{{E}_{a}}\] and enthalpy of reaction is \[\Delta H\](both of these in kJ/mol). Minimum value of \[{{E}_{a}}\] will be

A) less than \[\Delta H\]   

B) equal to \[\Delta H\]

C)                        more than \[\Delta H\] 

D)        equal to zero

Correct Answer: C

Solution :

Key Idea In endothermic reactions, energy of reactants is less than that of the products. Potential energy diagram for endothermic    reactions is                                   where,\[{{E}_{a}}=\] activation energy of forward  reaction \[E{{'}_{a}}=\] activation energy of backward reaction \[\Delta H=\] enthalpy of the reaction From the above diagram,                                                     \[{{E}_{a}}=E_{a}^{'}+\Delta H\] Thus, \[{{E}_{a}}>\Delta H\]