When a fuel burns, a spark is needed to start the reaction. A minimum amount of energy is needed in order for a fuel to burn.
The minimum amount of energy needed for a reaction to take place is called the activation energy.
In order for two substances to react, their particles must collide with enough energy. The particles in a substance have a range of different energies.
The activation energy is shown as a 'hump' in the line, which:
The overall change in energy in a reaction is the difference between the energy of the reactants and products.
The diagram shows a reaction profile for an exothermic reaction.
Describe how a reaction profile shows that a reaction is exothermic.
In the reaction for an exothermic reaction, the overall change is negative. You can tell this because the products have less energy than the reactants, and the arrow showing the overall change in energy points downwards.
The diagram shows a reaction profile for an endothermic reaction.
Describe how a reaction profile shows that a reaction is endothermic.
In the reaction for an endothermic reaction, the overall change is positive. You can tell this because the products have more energy than the reactants, and the arrow showing the overall change in energy points upwards.
A catalyst is a substance that:
A catalyst allows an alternative reaction pathway that has a lower activation energy than the uncatalysed reaction. This is seen in the reaction profile as a lower 'hump' representing the activation energy.