|Class 12 Chemistry Chemical Kinetics||Collision theory|
The molecules of the reacting species collide through the space in a rectilinear motion.
Rate of a chemical reaction is proportional to the number of collisions between the molecules of the reacting species.
The molecules must be properly oriented.
Let A+B --> C + D
Rate = ZABe-Ea/RT
Here ZAB = collision frequency of A and B.
Where p= steric factor which takes into account the proper orientation of the molecules participating in a chemical reaction.
PROBLEM. The activation energy for the reaction 2HI(g) → H2 + I2(g) is 209.5 kJ mol-1 at 581 K. Calculate the fraction of molecules of reactants having energy equal to or greater than activation energy?
SOLUTION. Ea = 209.5 kJ mol - 1 = 209500 J mol - 1
T = 581 K
R = 8.314 JK - 1 mol - 1
Fraction of molecules of reactants having energy equal to or greater than activation energy is as follows:
x = e-Ea/RT
ln x = -Ea/RT
log x = Ea/2.303RT
log x = 209500 J mol-1/2.303 X 8.314 J K-1 mol-1 X 581 = 18.8323
x = antilog (18.323)
= antilog 19.1977
= 1.471 X 10-19