Rate of reaction
The rate of a reaction is a measure of how quickly a A substance that reacts together with another substance to form products during a chemical reaction. is used up, or a A substance formed in a chemical reaction. is formed.
Collision theory
For a chemical reaction to happen:
- A general term for a small piece of matter. For example, protons, neutrons, electrons, atoms, ions or molecules. must collide with each other
- the particles must have enough energy for them to react
A collision that produces a reaction is called a A collision between reactant particles that has enough energy for a reaction to happen.. The The minimum amount of energy that colliding particles must have for them to react. is the minimum amount of The capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow. needed for a collision to be successful. It is different for different reactions.
Image caption, Colliding particles
1. Two pairs of particles move towards each other
1 of 3
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.
The mean rate of reaction can be calculated using either of these two equations:
\(mean~rate~of~reaction = \frac{quantity~of~reactant~used}{time~taken}\)
\(mean~rate~of~reaction = \frac{quantity~of~product~formed}{time~taken}\)
Measuring mass
The change in The amount of matter an object contains. Mass is measured in kilograms (kg) or grams (g). 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 The sum of the relative atomic masses of the atoms in a chemical formula., Mr.
The units for rate are usually g/s or g/min.
Measuring volume
The change in The volume of a three-dimensional shape is a measure of the amount of space or capacity it occupies, eg an average can of fizzy drink has a volume of 330 ml. of a reactant or product can be followed during a reaction. This method is useful when a gas leaves the reaction container. The volume of a gas is measured using a gas syringe, or an upside down Long glass tube with a tap and marked with volume measurements, used in titrations. or measuring cylinder.
The units for rate are usually cm3 s-1 or cm3 min-1.
Graphs
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 Another word for steepness. On a graph, the gradient is defined as being the change in the 'y' value divided by the change in the 'x' value. It defines how steep a line is. of the line is equal to the rate of reaction:
- the steeper the line, the greater the rate of reaction
- fast reactions - seen when the line becomes horizontal - finish sooner than slow reactions
Units for rates of reaction - Higher
The rate of a chemical reaction can also be measured in Mol s-1.