Chem. Unit 4, Chapter 1 - Kinetics

A summary of the kinetics chapter of unit 4 chemistry.

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  • Created by: Ajay
  • Created on: 07-01-13 20:06
Preview of Chem. Unit 4, Chapter 1 - Kinetics

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Ajay Rai
Reaction kinetics:
The rate of a chemical reaction is the change in molar concentration of a substance in unit time.
Collision theory ­ in gas, liquid or solution, particles are constantly moving and colliding with
each other. The distribution of energies between particles in a system is called the
MaxwellBoltzmann distribution.
The collision theory states that chemical reactions occur when particles have sufficient energy to
break existing chemical bonds and form new ones. The activation energy, EA, is required for this.
Temperature ­ increasing the temperature increases the number of collisions between particles
that possess energies equal to or greater than the activation energy. An increase in temperature
of 10K approximately doubles the reaction rate.
Surface area ­ increasing surface area makes the reaction occur faster. Collisions only occur at
the surface of a solid, so if a greater surface area is exposed there are more locations for
collisions to occur.
Concentration ­ increasing the concentration of a reactant means there are more particles in a
given volume. So the number of particles with energies greater than or equal to the activation
energy is greater.
Deriving the rate equation:
Rate of reaction ­ the rate at which a reactant is used up or a product is formed. This is
measured in concentration.
The rate of reaction is proportional to the concentration of A.
Rate = k x concentration of A rate = k[A].
The general rate equation for two reactants is rate = k[A]m[B]n.
Zero order reactions ­ the power zero is used in the rate equation. This is because the rate
does not change when the concentration of the reactant changes.
Rate = k[A]x.
The expression must equal 1 so rate = k[A]0 and therefore rate = k.
Kinetics

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Ajay Rai
First order reactions ­ when the rate of a reaction is directly proportional to the concentration
of one species.
Rate = k[A]1 so rate = k[A].
This is a first order reaction with respect to A. If the concentration doubles, the reaction rate
doubles.
Rate = = slope of curve.
Rate determining step ­ the rate determining step is the slowest stage in the reaction. Any
reaction can only proceed at the speed of the slowest stage.…read more

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