Q.Give a detailed account of the Collision theory of reaction rates of bimolecular reaction.
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Start your 14-day free trial to unlock the full solution →In collision theory, a bimolecular reaction rate depends on the collision frequency, the fraction of collisions with energy >= Ea, and a steric (orientation) factor: Rate = P Z_AB e^(-Ea/RT).
The collision theory of reaction rates was developed by Max Trautz and William Lewis. It treats reactant molecules as hard spheres and assumes that a reaction occurs only when molecules collide.
Main postulates (for a bimolecular reaction A + B -> products):
- Reaction through collisions:
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Reactant molecules must collide with one another for a reaction to occur. The number of collisions per second per unit volume is called the collision frequency (Z_AB).
- Not every collision is effective — the energy barrier:
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Only collisions in which the colliding molecules possess a certain minimum energy, equal to or greater than the activation energy (Ea), result in a reaction. These are called effective collisions.
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The fraction of molecules having energy >= Ea is given by the Boltzmann factor e^(-Ea/RT).
- Proper orientation — the steric factor:
- Even energetic collisions lead to products only if the molecules are correctly oriented at the moment of impact, so that the bonds that must break and form are properly aligned.
- This requirement is accounted for by the probability or steric factor P.
Rate expression:
- Combining these ideas, the rate of a bimolecular reaction is: …
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