The rate of a reaction is a measure of how quickly a reactant is used up, or a product is formed
For a chemical reaction to happen:
Reactant particles must collide with each other
The particles must have enough energy for them to react
A collision that produces a reaction is called a successful collision
Activation energy is the minimum amount of energy needed for a collision to be successful. This is different for different reasons
There are different ways to determine the rate of a reaction, depending on the reactants and products involved, and how easy it is to measure changes in them
How long a reaction is observed for depends on the rate of reaction, which can vary from being almost instantaneous to taking years to complete
In the lab, reactions are usually followed over a few seconds or minutes
Measuring mass:
Change in mass of a reactant or product can be followed during a reaction
Useful when carbon dioxide is a product leaving the reaction container
Not suitable for hydrogen and other gases with a small relative formula mass, Mr
Units for rate are usually g/s or g/m
Measuring volume:
Change in volume of a reactant or product can be followed during a reaction
This method is used when a gas leaves the reaction container
Volume of a gas is measured using a gas syringe, or an upside down burette or measuring cylinder
Units for rate are usually cm3/s or cm3/min
The rate of reaction can be analysed by plotting a graph of mass or volume of product formed against time. The graph shows this for two reactions.
The gradient of the line is equal to the rate of reaction:
the steeper the line, the greater the rate of reaction
fast reactions finish sooner (when the line becomes horizontal) than slow reactions
