A heating or cooling curve graphically represents the relationship between heat, temperature, and the physical state of a substance. The curve has sloped sections where the temperature changes as heat is added, and the substance remains in a single phase (solid, liquid, or gas). The formula q=mcΔT is used to calculate the heat involved in these sections. The curve also has flat plateaus where the temperature remains constant because the added heat is used entirely for a phase change, such as melting or boiling. The formula q=nΔH is used for these sections. The vaporization plateau is longer than the melting plateau because it takes more energy to fully break intermolecular forces to turn a liquid into a gas.