Rate of reaction 1 – reaction rates
Reaction rates
The rate of reaction measure how much product is formed in a fixed period of time.
Fast and slow reactions:
Rusting is a slow reaction.
Burning and explosions are fast reactions.
3
The mass of a product formed is measured in grams and the volume of a product is measured in cm -
3 3
measured in seconds or minutes - g/s or g/min and cm /s or cm /min.
Measuring rates
The rate of reaction can be worked out using the gradient of a graph. Gradient = change in y
Change in x
Limiting reactants
Reactions stop when all the particles of one of the reactants are all used up. At the end of the reaction the
limiting reactant will be all used up due to it not being in excess.
Example - Magnesium and hydrochloric acid react together, when the reaction is over – magnesium is the
limiting reactant if it is all gone at the end, and hydrochloric acid is the limiting reactant if some magnesium is
left at the end.
The amount of product formed is directly proportional to the amount of limiting reactant used - e.g. If amount
of limiting reactant doubles, then the amount of product formed, doubles.
Reactions occur when particles collide together. So if the number of reacting particles of one reactant is
limited, the number of collisions by particles of that reactant is limited.
Rate of reaction 2 – reaction rate and changing conditions
Collision theory
For a chemical reaction to occur the particles must collide with each other. A collision with too little energy will
not create a reaction. The colliding particles will not have enough energy for the collision to be successful.
The rate of reaction depends on the amount of successful collisions between reactant particles – if the
particles have lots of energy the more successful collisions, resulting in a faster rate of reaction.
Collision frequency – is the number of successful collisions between reacting particles.
Effect of temperature
The increase of the temperature increases the kinetic energy of the particles. Increasing the kinetic energy
makes the particles move more and faster – therefore increasing the chance of them colliding with the other
react and increases the chance in which the collision is successful.
Effect of concentration
The concentration of a reactant increases the amount of particles, meaning they become more crowded –
therefore increasing the number of collisions.
Effect of pressure
An increase in the pressure decreases the volume in which the same amount of reactants are contained –
forcing the particles closer together and increasing the rate of reaction due to an increase in the number of
collisions.
Reaction rates
The rate of reaction measure how much product is formed in a fixed period of time.
Fast and slow reactions:
Rusting is a slow reaction.
Burning and explosions are fast reactions.
3
The mass of a product formed is measured in grams and the volume of a product is measured in cm -
3 3
measured in seconds or minutes - g/s or g/min and cm /s or cm /min.
Measuring rates
The rate of reaction can be worked out using the gradient of a graph. Gradient = change in y
Change in x
Limiting reactants
Reactions stop when all the particles of one of the reactants are all used up. At the end of the reaction the
limiting reactant will be all used up due to it not being in excess.
Example - Magnesium and hydrochloric acid react together, when the reaction is over – magnesium is the
limiting reactant if it is all gone at the end, and hydrochloric acid is the limiting reactant if some magnesium is
left at the end.
The amount of product formed is directly proportional to the amount of limiting reactant used - e.g. If amount
of limiting reactant doubles, then the amount of product formed, doubles.
Reactions occur when particles collide together. So if the number of reacting particles of one reactant is
limited, the number of collisions by particles of that reactant is limited.
Rate of reaction 2 – reaction rate and changing conditions
Collision theory
For a chemical reaction to occur the particles must collide with each other. A collision with too little energy will
not create a reaction. The colliding particles will not have enough energy for the collision to be successful.
The rate of reaction depends on the amount of successful collisions between reactant particles – if the
particles have lots of energy the more successful collisions, resulting in a faster rate of reaction.
Collision frequency – is the number of successful collisions between reacting particles.
Effect of temperature
The increase of the temperature increases the kinetic energy of the particles. Increasing the kinetic energy
makes the particles move more and faster – therefore increasing the chance of them colliding with the other
react and increases the chance in which the collision is successful.
Effect of concentration
The concentration of a reactant increases the amount of particles, meaning they become more crowded –
therefore increasing the number of collisions.
Effect of pressure
An increase in the pressure decreases the volume in which the same amount of reactants are contained –
forcing the particles closer together and increasing the rate of reaction due to an increase in the number of
collisions.
