Question

2. How does a particles energy change as it changes state?

Answer 1

When a substance is heated, it gains thermal energy. Therefore, its particles move faster and its temperature rises. When a substance is cooled, it loses thermal energy, which causes its particles to move more slowly and its temperature to drop.
In chemistry, a pure substance is a sample of matter with both definite and constant composition and distinct chemical properties. To avoid confusion, a pure substance is often referred to as a "chemical substance."