For a chemical reaction to happen:
A collision that produces a reaction is called a successful collision. The 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. The method chosen usually depends on the reactants and products involved, and how easy it is to measure changes in them.
In addition, how long a reaction is observed for depends on the rate of reaction. Reactions can vary from being almost instantaneous to taking years to complete. In the lab, reactions are usually followed over a few seconds or minutes.
Rusting is a slow reaction. Give four examples of a very fast reaction.
Combustion, explosions, neutralisation reactions and precipitation reactions are very fast reactions.
The change in mass of a reactant or product can be followed during a reaction. This method is useful when carbon dioxide is a product which leaves the reaction container. It is not suitable for hydrogen and other gases with a small relative formula mass, Mr. The units for rate are usually g/s or g/m.
The 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. The volume of a gas is measured using a gas syringe, or an upside down burette or measuring cylinder. The 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: