In a chemical reaction, things called reactants change into products. This happens through different steps where chemical bonds are broken and formed. We can write this transformation using a balanced chemical equation. This equation shows how much of the reactants and products are involved. Let’s look at some important ideas about this process:

1. Conservation of Mass: This means that the total weight of the reactants has to equal the total weight of the products. For example, in a simple reaction:
   $\text{A} + \text{B} \rightarrow \text{C} + \text{D}$
   the weight of A and B is the same as the weight of C and D.

2. Mole Ratios: Stoichiometry helps us use numbers in a balanced chemical equation to find out how many moles of each substance we have. For example, in this equation:
   $2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}$
   we see that the ratio of hydrogen (H₂) to water (H₂O) is 2:2, which is the same as 1:1.

3. Energy Changes: Chemical reactions usually involve changes in energy. Some reactions take in energy, which are called endothermic reactions, while others give off energy, known as exothermic reactions. These energy changes can also affect how fast a reaction happens and how much product we get.

By understanding these ideas, students can make predictions about how reactants will turn into products in different chemical reactions.