Conservation of mass is a key idea in chemistry. It means that mass cannot be created or destroyed during a chemical reaction. This concept is very important for understanding how different substances change when they react with each other.

Here’s why it is important:

1. Tracking Mass: In any reaction, the mass of the starting materials (called reactants) must equal the mass of the substances formed (called products). For example, if we start with 10 grams of reactants, we should end up with 10 grams of products.

2. Predicting Outcomes: Knowing that mass stays the same helps scientists predict how much product will be made. For example, if you mix 2 grams of hydrogen with 16 grams of oxygen, you will create 18 grams of water.

3. Balancing Equations: To make sure the conservation of mass is followed, chemical equations need to be balanced. For instance, in this reaction: $2H_2 + O_2 \rightarrow 2H_2O$ the number of atoms on both sides is equal.

In short, conservation of mass helps us understand chemical reactions better. It is also very important for doing experiments safely and accurately!