4.2a Heat moves in predictable ways, flowing from warmer objects to cooler ones, until

both reach the same temperature.

4.2b Heat can be transferred through matter by the collisions of atoms and/or mole-

cules (conduction) or through space (radiation). In a liquid or gas, currents will facilitate

the transfer of heat (convection).

4.2c During a phase change, heat energy is absorbed or released. Energy is absorbed

when a solid changes to a liquid and when a liquid changes to a gas. Energy is released

when a gas changes to a liquid and when a liquid changes to a solid.

4.2d Most substances expand when heated and contract when cooled. Water is an

exception, expanding when changing to ice.

4.2e Temperature affects the solubility of some substances in water.