The speed of a chemical reaction is affected by temperature, concentration, particle size and the presence of a catalyst. It can be calculated by measuring changes in reactants/products.
For a reaction to occur, the particles that are reacting must collide with each other. Only some of all the collisions that take place cause a chemical change to happen. These are called 'successful' collisions. The greater the number of 'successful' collisions, the faster the rate of a reaction. This is called the 'collision theory'.
There are four factors that affect the rate (speed) of a chemical reaction:
temperature
concentration
particle size
use of a catalystCatalysts are substances that speed up chemical reactions but can be recovered chemically unchanged at the end of the reaction.