Endothermic and Exothermic Reactions

We all know that an exothermic reaction gives off energy in the form of heat, light, or sound, and that an endothermic reaction absorbs energy.  If the reaction takes more energy to break the bonds that hold molecules together, it is endothermic. If it takes less energy, the reaction is exothermic.

ENTHALPY, or "H", is the sum of all kinetic and potential energies in a system.  You will see this term used many times.

Change in enthalpy is denoted as 'delta' H.

Exothermic reactions result in a negative enthalpy, or negative "H".  Also, endothermic reactions are characterized by a positive heat flow, or positive "H".

An example of an endothermic reaction is photosynthesis. Plants convert CO2 and water into oxygen and glucose from the energy from the sun.
The general formula of an endothermic reaction is:
A + B + Energy --> AB


The burning of any substance is an example of an exothermic reaction. 
The general form of an exothermic reaction is:
A + B --> AB + Energy


Energy diagrams tell us about the relative rate of a chemical reaction.   They are also called potential energy diagrams or chemical reaction energy reactions.
Here is an energy diagram of a exothermic reaction:

This is an energy diagram of an endothermic reaction:

where: (a) is the activation energy, which is the energy required to initiate a chemical reaction,
(b) is the change between the reactants and products,
and (c) is the change in energy, or enthalpy



  Check out this video! I hope it helps! 

Here is a FUN quiz about exothermic and endothermic that you can do :)http://www.softschools.com/quizzes/science/chemical_reactions/quiz380.html