In a chemical reaction, we start with substances that change called reactants. After the reaction happens, new substances are formed, which we call products. It's important to understand the difference between these two because it helps us see how things change in chemistry.

Reactants

• What are they? Reactants are the starting materials that are there before any change happens in the reaction.

• Example:

  • When methane ($CH_4$) burns with oxygen ($O_2$), both methane and oxygen are the reactants.

• Counting Them: We can measure how much of each reactant we have using numbers in balanced equations. For example, in this equation: $CH_4 + 2 O_2 \rightarrow CO_2 + 2 H_2O$ there is 1 part of methane and 2 parts of oxygen.

Products

• What are they? Products are the new substances that are created after the reaction is done.

• Example:

  • When methane burns, the products are carbon dioxide ($CO_2$) and water ($H_2O$).

• How Good Is the Reaction? We can measure how effective a reaction is by looking at the percent yield. We can calculate it this way: $\text{Percent Yield} = \left( \frac{\text{actual yield}}{\text{theoretical yield}} \right) \times 100$

Summary

In short, chemical reactions take reactants and turn them into products by rearranging atoms. Balancing equations is very important because it shows that the total weight of reactants matches the total weight of products. This follows the law of conservation of mass, which means matter cannot be created or destroyed in a reaction.