1. This is an endothermic reaction
Energy has been taken from the surroundings
This is the energy released when the bonds form
This is the activation energy.
The energy supplied to break the bonds
Products
Energy in the molecules bonds
The products are at a higher energy level, so energy has had to be taken in from the surroundings.
Reactants

2. Energy in the molecule’s bonds
This is the activation energy.
The energy supplied to break the bonds.
Energy in the molecule’s bonds
Reactants
This is the energy released when the bonds form.
Products
The products are at a lower energy level, so energy has had to be released to the surroundings.
This is an exothermic reaction. Energy has been released to the surroundings

3. Energy in the molecule’s bonds
A catalyst lowers the activation energy and thus speeds up chemical reactions
Energy in the molecule’s bonds
The overall energy changes however remain the same
Remember the catalyst does not get used up in the reaction so is use over and over again

4. Therefor this is an endothermic reaction
2H2O  2H O2
Therefor this is an endothermic reaction
y-This is the energy released when the bonds in the hydrogen and oxygen form
Energy in the molecule’s bonds
x-This is the activation energy.
The energy supplied to break the bonds in the water
Products
z-The products are at a higher energy level, so energy has had to be taken in from the surroundings.
=486kJ is absorbed from the surroundings
Reactants