1. Energy in chemical reactions
Chapter 3.3

2. Chemical reactions release or absorb energy
Bond Energy: the energy associated with chemical bonds.
Breaking a bond between atoms requires a certain amount of energy.

3. Exothermic reaction
If more energy is released when the products form than is needed to break the bonds in the reactants, then energy is released during the reaction.
Exothermic Reaction: a reaction in which energy is released

4. Exothermic reactions Produce an increase in temperature
Energy is released as heat or light
Combustion reactions are exothermic
Glow sticks, fireflies, some species of fish and jellyfish

5. Endothermic reaction
If more energy is required to break the bonds in the reactants than is released when the products from, then energy must be added to the reaction.
Endothermic Reaction: a reaction in which energy is absorbed

6. Endothermic reactions
Produce a decrease in temperature
Energy is absorbed from the surroundings
Photosynthesis, where plants absorb the energy from the sun to make sugar

7. Exothermic Reaction
Reactants  Products + Energy
Endothermic Reaction
Reactants + Energy  Products

9. Exothermic and endothermic work together
If an exothermic reaction goes in the opposite direction, it becomes an endothermic reaction, and vise versa.
The energy in sunlight is stored by endothermic reactions. When it is needed, it is released by exothermic reactions.
This forms a cycle of energy storage and use on Earth.