Describe the difference between composition and decomposition reactions.

Composition and decomposition reactions are two fundamental types of chemical reactions.

1. Composition Reaction: A composition reaction (also known as a combination or synthesis reaction) is a reaction where two or more substances combine to form a single, more complex substance. The general form of a composition reaction is A + B -> AB. For example, when hydrogen gas (H2) reacts with oxygen gas (O2), they combine to form water (H2O).

2. Decomposition Reaction: A decomposition reaction is the opposite of a composition reaction. It is a reaction in which a single, complex substance breaks down into two or more simpler substances. The general form of a decomposition reaction is AB -> A + B. For example, when electricity is passed through water (H2O), it breaks down into hydrogen gas (H2) and oxygen gas (O2).

In summary, the key difference between composition and decomposition reactions is that in composition reactions, substances combine to form a new one, while in decomposition reactions, a substance breaks down into two or more simpler substances.