1. What Is a Chemical Reaction?

In a chemical reaction, one or more substances change into new substances with different properties. The bonds between atoms break and re-form, rearranging the atoms into new combinations.

Chemists write reactions as an equation:

• The reactants are the starting substances (on the left).
• The products are the new substances formed (on the right).
• The arrow (→) means 'yields' — reactants form products.

How can you tell a chemical reaction happened? Look for the signs: a color change, gas or bubbles forming, a temperature change (or light), a precipitate (a solid appearing in a liquid), or a new odor.

⚠️ Common misconception: atoms are not created or destroyed in a reaction. They are just rearranged — the same atoms end up in new substances.

💡 Tip: reactants → products. Bonds break and re-form; watch for signs like bubbles, color change, or heat.