Exothermic reactions give out energy to their surroundings. The energy of the products is less than the energy of the reactants.
Some exaples of Exothermic reactions are: respiration and burning.
Endothermic reactions take in energy from their surroundings. The energy of the products is greater than the energy of the reactants.
An example of an Endothermic reaction is : Photosynthesis.
Breaking and Making bonds.
In chemical reactions chemical bonds break. Bond breaking takes in energy so it is Endothermic.
Then new bonds are made. bond making gives out energy is it is an Exothermic reaction.
If the energy taken in to break bonds is less than the energy given out making bond the reaction is Exothermic.
If the energy taken in to break bonds is greater than the energy given out making bonds the reaction is Endothermic.
We can work out the energy transfer like this:
Energy transfer= Energy taken in to break bonds - energy given out making bonds
Activation energy is the energy needed for the reaction to begin colliding molecules.
A Catalyst can lower the activation energy, this is shown with the blue line.