Give example of a chemical change which occurs by the action of heat.

Answer

### Step-by-Step Solution:

1. **Understanding Chemical Changes**: A chemical change is a process where one or more substances are transformed into new substances with different properties. This often involves a reaction that produces new materials.

2. **Identifying a Chemical Change by Heat**: One common example of a chemical change that occurs due to the action of heat is the decomposition of lead(II) nitrate (Pb(NO3)2).

3. **Chemical Reaction**: When lead(II) nitrate is heated, it undergoes a decomposition reaction. The balanced chemical equation for this reaction is:
\[ 2 \, \text{Pb(NO}_3\text{)}_2 \, \xrightarrow{\text{heat}} 2 \, \text{PbO} + 4 \, \text{NO}_2 + \text{O}_2 \]
This indicates that when lead(II) nitrate is heated, it breaks down into lead(II) oxide (PbO), nitrogen dioxide (NO2), and oxygen (O2).

4. **Observing the Products**:
- **Lead(II) Oxide (PbO)**: This is a solid and has different properties compared to lead(II) nitrate.
- **Nitrogen Dioxide (NO2)**: This is a brown gas, which is also different from the original compound.
- **Oxygen (O2)**: This is a colorless gas that is released during the reaction.

5. **Conclusion**: The heating of lead(II) nitrate results in the formation of new substances (PbO, NO2, and O2) which have different physical and chemical properties from the original compound (Pb(NO3)2). This exemplifies a chemical change induced by heat.