AS CHEM2 - Kinetics

Kinetics revision notes

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  • Created on: 18-06-11 22:24
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Kinetics
Rate of reaction:
Decrease in the concentration of reactants per unit time, or the increase in the concentration of products per
unit time
Collision Theory:
If a successful chemical reaction is to take place between two particles, they must first collide with sufficient
energy and with the correct orientation to bring the active sites together.
1) Collision frequency
The number of collisions between particles per unit time. It can be altered by changing the concentration of the
reactants, by changing the total pressure, by changing the temperature or by changing the size of the reacting
particles.
2) Collision energy
The combined energy of the colliding particles. Not all the particles in a given system have the same energy;
they have a broad distribution of different energies. The shape of the distribution of energies depends on the
temperature of the system: the higher the temperature, the greater the mean kinetic energy of the particles.
3) Activation energy
The minimum energy the colliding particles need in order to start the reaction. It can be altered by the addition
of a catalyst.
The greater the fraction of collisions that result in a chemical reaction, the faster the reaction will be. The
fraction of successful collisions can be increased by increasing the collision energy or decreasing the activation
energy.
FACTORS AFFECTING THE RATE OF REACTION:
Fraction of
Collision Collision Activation
Effect on: successful Rate
frequency energy energy
collisions

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Decrease particle
Increases No effect No effect No effect Increases
size (solids only)
Increase
concentration
Increases No effect No effect No effect Increases
(liquids and
gases)
Increase pressure
Increases No effect No effect No effect Increases
(gases)
Increase
Increases Increases No effect Increases Increases
temperature
Add a catalyst No effect No effect Decreases Increases Increases
1) Particle size
A decrease in particle size increases the rate of reaction because:
- The surface area increases (more solid particles are exposed to the other reactants)
- The…read more

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The collision frequency increases as they collide more often
The higher the activation energy, the greater the effect an increase in temperature will have.
A small increase in temperature greatly increases number of particles with greater energy than the activation
energy.
5) Catalyst
A catalyst is a substance which changes the rate of a chemical reaction without itself being chemically altered at
the end of the reaction.…read more

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