Chemical Kinetics and Nuclear ChemistryHard

Question

Following are the values of Ea and DH for three reactions carried out at the same temperature :
    I :  Ea = 20 kJ mol-1, ᐃH = - 60 kJ mol-1
    II : Ea = 10 kJ mol-1, ᐃH = - 20 kJ mol-1
    III: Ea = 40 kJ mol-1, ᐃH = + 15 kJ mol-1    
If all the three reaction have same frequency factor then fastest and slowest reactions are :

Options

A.Fastest → I    Slowest → II
B.Fastest → II    Slowest → III
C.Fastest → I    Slowest → III
D.can′t be predicted.

Solution

The rate of reaction is decided by value of rate constant which depends on energy of activation not on the value of ᐃH, definitely the comparison of rate of reactions of backward reactions can be done if ᐃH values are also given to us.

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