Question

4. (10 pts) Several factors aflecet the rates of chemical reactions. Thehemic torstsc have on rates can usually be explained using the collision thNa ffects a) Briefly describe the collision theory of chemical reactions to explaint affect the rate of chemical reactions and use collision theory factors have on the rate of reactions. The a feet these factors ur factors that fects t to exp

Answer 1

Main points of collision theory as follows
1.A reaction occurs only when the reactant molecules encounter
together
2.All collision are not effective.Only effective collision
of reactants results in the formation of products
3.Effective collisions happen only when reactant molecule
acquire definite amount of energy. The minimum amount of
energy which mustbe possesed by reactants to make effective collision
is called THRESHOLD ENERGY.

b. The 4 factors which affect rate are as follows
1.nature of reactants - Rate depends on nature of reactant.For example
if reaction involve ionic[polar] substance it happens higher
speed.Whereas in covalent compound rate is low.Because
covalent compounds involves breaking of old bond and formation of new bonds
Or rate depends on rearrangement of bonds.If these rearrangement happens
easily [requires less energy] then rate will be fast.
2.Concentration of reactants -Usually rate increases with
increasing the concentration of reactants.According to collision theory
when concentration of reactant increased,possibility of
molecular collisions increases.Hence rate of reaction increases
3.Temperature-Rate of reaction increases with increase in
temperature.According to collision theory,only those reactants having threshold energy
can produce product through effective collision. When temperature
increases kinetic energy of molecule increases.This increase fraction of molecules having
energy greater than or equal to the threshold energy.
Hence increase in temperature increases effective collision,resulting in an
increase in rate
4.presence of catalyst-Catalyst is a substance that increases
rate of reaction without taking part in the reaction.According
to collision theory when a catalyst is used the reaction proceeds
through an alternative path with a lower energy barrier.
It happens by the formation of activated complex with catalyst having lower
energy which enables large number of reactant molecules to cross energy
barrier. Hence rate increases considerably.

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