Class 12 Chemistry Chemical Kinetics Activation energy

Activation energy

• The minimum quantitiy of external energy required for the conversion of reactant into product or to produce an unstable intermediate is called activation energy. It is E
• Rate of reaction is inversely proportional to the activation energy.
• Therefore, greater value of activation energy leads to lower rate of reaction and increased influence of temperature change on the rate constant. PROBLEM.   The rate of the chemical reaction doubles for an increase of 10 K in absolute temperature from 298 K. Calculate ESolution

SOLUTION.   It is given that T1 = 298 K

∴T2 = (298 + 10) K

= 308 K

We also know that the rate of the reaction doubles when temperature is increased by 10°.

Therefore, let us take the value of k1 = k and that of k2 = 2k

Also, R = 8.314 J K - 1 mol - 1

Now, substituting these values in the equation:

Log k2/k1 = Ea/2.303R [T2-T1/T1T2]

Log 2k/k = Ea/2.303 X 8.314 [10/298 X 308]

Ea= 2.303 X 8.314 X 298 X 308 X log2/10

= 52897.78 J mol - 1

= 52.9 kJ mol - 1

.