Chemical Reactions Section 2.4

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.

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

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

Example

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.

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