When crayons and candles are heated, they undergo a change in phase from solid to liquid. This change in phase is a physical change that alters the physical properties of the materials. The solid wax in a candle melts and burns when it is heated, and the wax combines with oxygen from the atmosphere and is converted into carbon dioxide and water vapor. Similarly, when crayons are heated, they melt and become a liquid, which can then be used to create art. Once the melted wax cools down, it solidifies and returns to its original state.