Question

When a substance is heated, what causes its properties to change?

Answer 1

Molecule movement. Ice is so hard because molecules are not moving, and the space between them are small. Hot water has bigger space between molecules that are always in motion.

Answer 2

The molecules vibrate when the substance is heated, and the shape of the substance begins to form a different shape. For example: when you hear up metal it will melt becuase its molecules are changing and moving.