Advanced Topics
In a nutshell: Chemical reactions transform substances, and equations help us track what happens.
## Making and Breaking Bonds
A **chemical reaction** is when substances (called reactants) change into new substances (called products). During this process, chemical bonds are broken and new ones are formed.
### Writing Chemical Equations
Chemists use equations to show what happens in a reaction. For example, when hydrogen and oxygen make water:
\[
2H_2 + O_2 \rightarrow 2H_2O
\]
The arrow shows the direction of the reaction, from reactants to products.
### Types of Chemical Reactions
- **Combination:** Two or more substances join to form one (e.g., iron and oxygen make rust).
- **Decomposition:** One substance breaks apart (e.g., water splitting into hydrogen and oxygen).
- **Replacement:** Elements switch places (e.g., zinc and hydrochloric acid make zinc chloride and hydrogen).
Chemical reactions are everywhere—from baking bread to powering cars!
Examples
- Burning methane gas produces carbon dioxide and water.
- Mixing vinegar and baking soda creates bubbles of carbon dioxide gas.