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Effect Of Temperature On Rate Of A Reaction

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Effect Of Temperature On Rate Of A Reaction - Lesson Summary

The rate of a reaction depends on the concentration of its reactants (or) on the pressure in case of gaseous reactants. Along with concentration or pressure, temperature also has a major effect on the rate of a reaction.

The rate of a reaction generally increases with an increase in the temperature.

The Arrhenius equation gives the relationship between the rate constant (k) of a reaction and the absolute temperature (T).

Rate of Reaction ∝ Temperature

According to the collision theory only a small fraction of the collisions produce a reaction. These colliding molecules must collide with the proper orientation with sufficient energy, called threshold energy, which is the energy possessed by reacting species in addition to activation energy.

The energy required by the reactant molecules to reach the transition state is known as activation energy Ea.

According to the collision theory, only a small fraction of the collisions produce a reaction. Therefore the colliding molecules must collide with the proper orientation with sufficient energy, called threshold energy, which is the energy possessed by reacting species in addition to activation energy.

According to the Arrhenius equation,

      k = A e-Ea/RT

Where k = Rate Constant
          A = Frequency Factor
          Ea = Activation Energy
          R = Gas Constant
          T = Absolute Temperature

In the Arrhenius equation Ea/RT, corresponds to the fraction of molecules that have kinetic energy greater than Ea.

                  k = A e-Ea/RT

Logek = -Ea/RT + LogeA .....(1)

Log k = -Ea/2.303RT + Log A ......(2)

At Temperature T1:
 Log k1 = -Ea/2.303RT1 + Log A .....(2a)

At Temperature T2:
 Log k2 = -Ea/2.303RT2 + Log A .....(2b)

Subtracting Eq (2a) from Eq(2b), results in

 Log k2 -  Log k1 = Ea/2.303RT1 - Ea/2.303RT2

 Log ( k2 / k1) = Ea/2.303R [1/T1 - 1/T2]

 Log ( k2 / k1) = Ea/2.303R [(T2 - T1)/T1.T2]

Thus Arrhenius equation is useful to calculate the activation energy at different temperatures by using known experimental values of the rate constants.

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