1.1 The particles in a chemical reaction must collide
together for a reaction to take place. The more collisions
there are, the faster the reaction. The idea of collisions
is used to explain how different factors affect the rate of
2 Temperature of the Reactants
2.1 Lower temperature - Lower rate. In a cold
reaction mixture the particles move quite slowly
because they have less kinetic energy. The
particles will collide with each other less often
and with less energy, so there will be less
effective collisions per second
2.2 Higher temperature - higher rate. If the
temperature is increased, the particles will
move faster because they have more kinetic
energy. They will collide with each other
more often and with greater energy, so there
will be more effective collisions per second.
3 Concentration of the Reactants
3.1 Lower concentration - lower rate. In a
reaction where one or both reactants are in
low concentrations, the particles are spread
out. The particles will collide with each other
less often, resulting in fewer effective
collisions per second.
3.2 Higher concentration - higher rate. Where
there are high concentrations of one or
both reactants, the particles are crowded
close together. The particles will collide
with each other more often, resulting in
more effective collisions per second.
4 Pressure of Gas
4.1 Low pressure- low rate. When gas is
under a low pressure, the particles will
collide with each other less often resulting
in fewer effective collisions pre second.
4.2 Higher pressure - higher rate. When the
pressure is high, the particles are
crowded more closely together. The
particles collide more often, resulting in
many more effective collisions per second
5 Collision Theory LT
5.1 You may be asked to interpret information
about the effect of changing temperature,
concentration or pressure on a reaction. This
could be in tables, graphs or a description.
5.2 You may be asked to sketch a graph showing
the effect of changing variables. Such as
temperature, pressure or concentration.
6 Collision Theory
6.1 Increasing temperature causes an increase in the kinetic energy of the particles, they move a lot faster. The faster the particles
move, the number of collisions per second increases. The more collisions there are between particles, the faster the reaction.
6.2 When the particles collide at an increased temperature they have more energy. When a collision has more energy, the chance of it causing a successful collision is increased.