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A substance may react quickly or slowly with another substance. How fast a reaction occurs is called its reaction rate. An example of a fast reaction rate is an explosion. An example of a slow reaction rate is rusting.
Reaction rate can be measured by timing how long it takes for a reactant to be used up, or by measuring how quickly the product is formed.
A reaction rate curve can be plotted to show the speed of a reaction.
All matter is made up of tiny particles which are constantly in motion. This is known as the particle theory or kinetic theory. Particles can be atoms, molecules or ions that make up a substance. The amount of movement of these particles depends on which state the particles are in, that is, whether they are solids, liquids or gases.
Solid particles have low energy vibrations only. Liquid particles have more kinetic energy (movement energy), so these particles can flow past each other. Gas particles have high energy and move rapidly in all directions.
Temperature affects the speed of the particles. When the temperature increases the speed of the particles increases.
Water is a substance that can be found on Earth in all three states of matter- solid water (ice), liquid water, and water as a gas in steam or in the atmosphere.
The collision theory helps explain how reactions between particles begin and why the rate of reaction can change.
The collision theory states that for a reaction to occur:
There must be a collision between the reacting particles.
The particles must collide with sufficient energy to break forces holding particles together. This energy is called the activation energy. If the energy of a collision is not great enough, the reaction will not occur.
The particles must collide in the correct orientation (or position).