Answer

For some materials chemical changes rather than physical changes are initiated by heat. In chemical changes new substances are formed and the process is often difficult to reverse. During chemical changes particles do change with atoms or ions regrouping . Bonds (links) between atoms break and new ones form and energy is either given out or taken in. Some chemical changes are initiated by mixing.
The overall changes can be:

• Breakdowns where at a point of instability the constituent particles (molecules) might break down often as a result of heating
• Combinations of different types of particles to form new ones or