Question

According to the collision theory, only the effective collisions among the reacting species result in the products. In order that the collisions may be effective, the reacting species must have energy equal to or more than a certain minimum energy called threshold energy `(E^(@))`. Extra energy which has be supplied to the reactants to make collisions effective is known as activation energy `(E_(a))`. This is related to reaction rate with the help of Arrhenius equation, `k=Ae^(-Ea//RT)`
The equation also helps in calculating the activation energy for a reaction at a specific temperature. In general, the rate of reaction is inversely proportional to the activation energy required.
Consider the reaction `A to 2B + C, DeltaH=-15` kcal. The energy of activation of backward reaction is 20 kcal `mol^(-1)`. In presence of the catalyst, the energy causes the rate of the reaction to increase by the number of times equal to
A. `e^(3.5)`
B. `e^(2.5)`
C. `e^(-2.5)`
D. `e^(2.303)`

Answer 1

Correct Answer - B
b) `E_(a)(f) - E_(ab) = DeltaH=-15 kcal`
`E_(af) = -15 + 20=5kcal`
`(k("catalyst"))/(k) = e^(E_(a)-E_(a)("catalyst"))/(RT) = e^((5-3) xx 10^(3))/(2 xx 400)`
`=e^((2 xx 1000))/((2xx400))=e^(2.5)`