Q.Give a detailed account of the collision theory of reaction rates of bimolecular gaseous reactions.

Collision theory says a bimolecular gas reaction's rate depends on how often molecules collide, what fraction of collisions have enough energy (activation energy), and what fraction have the right orientation.

Collision theory (developed by Max Trautz and William Lewis) explains the rates of bimolecular gaseous reactions in terms of molecular collisions. Its main postulates:

1. For a reaction to occur, the reacting molecules (A and B, say) must collide with each other. The rate of reaction therefore depends on the frequency of collisions, Z_AB (the number of collisions between A and B molecules per unit volume per unit time).

2. However, not every collision leads to a reaction (only a small fraction do) - only "effective collisions" result in product formation. A collision is effective only if:

1. Sufficient energy criterion: the colliding molecules must possess a combined kinetic energy equal to or greater than a certain minimum value called the threshold energy. Molecules with energy less than the threshold simply bounce off without reacting. The fraction of collisions possessing this minimum required energy (activation energy, Ea) is given by the Boltzmann/Arrhenius factor e^(-Ea/RT) - as temperature increases, this fraction (and hence the rate) increases.
2. Proper orientation criterion: even if the colliding molecules have enough energy, the reaction will occur only if they collide with the correct spatial orientation, so that the specific bonds that must break and form are properly aligned. This is accounted for by a steric factor (or probability factor), P, which is generally less than 1. Combining these factors, the rate of a bimolecular gaseous reaction is given by: Rate = P x Z_AB x e^(-Ea/RT) where: Z_AB = collision frequency of reactants A and B …