Question

some substances, like chocolate or candle wax, can change from a solid to a liquid when heated and then change back to a solid when cooled. why do you think this happens?

Explanation:

Heating provides energy to break intermolecular forces in solids, changing them to liquids. Cooling reduces energy, allowing intermolecular forces to reform, changing them back to solids.

Answer:

This happens due to the change in intermolecular forces with temperature. Heating weakens them causing melting (solid - to - liquid), and cooling strengthens them causing solidification (liquid - to - solid).