In Grade 11 Chemistry, it’s important to know how to classify chemical reactions. This helps us understand the basics of the subject. One helpful way to classify these reactions is by looking at the reactants (the starting materials) and the products (the substances formed). Let’s break down the different types of reactions and how chemical equations can show us what’s happening.

1. Synthesis Reactions

In a synthesis reaction, two or more reactants come together to make one product.

It looks like this: $A + B \rightarrow AB$

Example: When hydrogen gas ($H_2$) and oxygen gas ($O_2$) join to create water ($H_2O$): $2H_2 + O_2 \rightarrow 2H_2O$

2. Decomposition Reactions

Decomposition reactions happen when one compound breaks apart into two or more simpler substances.

This can be shown like this: $AB \rightarrow A + B$

Example: If we pass electricity through water, it breaks into hydrogen gas and oxygen gas: $2H_2O \rightarrow 2H_2 + O_2$

3. Single Replacement Reactions

In a single replacement reaction, one element takes the place of another in a compound.

It looks like this: $A + BC \rightarrow AC + B$

Example: When zinc ($Zn$) replaces copper ($Cu$) in copper(II) sulfate: $Zn + CuSO_4 \rightarrow ZnSO_4 + Cu$

4. Double Replacement Reactions

In double replacement reactions, two compounds swap parts with each other.

It looks like this: $AB + CD \rightarrow AD + CB$

Example: When sodium sulfate reacts with barium chloride, barium sulfate and sodium chloride are formed: $Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 + 2NaCl$

5. Combustion Reactions

Combustion reactions happen when a substance reacts with oxygen and releases energy.

The general form looks like this: $C_xH_y + O_2 \rightarrow CO_2 + H_2O$

Example: When methane ($CH_4$) burns, it produces carbon dioxide and water: $CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O$

By looking at the reactants and products, you can sort these reactions into these five types. This gives you a better understanding of how different substances work together during chemical changes.