1. Chemical Reactions
Section 2.4

2. Chemical reactions
When chemical reactions happen bonds between atoms are formed or broken, substances change into different substances.
When this happens inside organisms, it is called metabolism.

3. Writing chemical equations
Substances that undergo chemical reactions are called reactants.
Substances formed are called products.

4. Writing chemical equations
Atoms are never created nor destroyed in a reaction, so equations must always be balanced.

5. Example

6. There is a certain amount of energy required to start a reaction called activation energy.
There is a certain amount of energy required to break a bond called bond energy.

7. Some Reactions release more energy than they absorb: they are exothermic.
Some reactions absorb more energy than they release: they are endothermic