Heating and cooling curves

In a nutshell

Heating and cooling curves can be used to explain how energy changes during a change in state.

Heating and cooling curves

Definition

Heating and cooling curves show energy changes during a change in state. These diagrams show how temperature change stops for a period of time when a material changes state.

A flat line on a heating or cooling curve indicates the temperature doesn't change.

Heating curve

The graph shows the relationship between time and temperature when a substance is heated.

Science; States of matter; KS3 Year 7; Heating and cooling curves

1.	When a substance is heated the temperature will rise.
2.	During melting or boiling, energy is being used to weaken forces between particles rather than raise the temperature. The temperature is constant, this is represented by a flat line on the heating curve.
3.	The flat line at the lower temperature represents the melting point of the solid and at the higher temperature represents the boiling point of the liquid.

Cooling curve

Below is a graph showing the relationship between time and temperature when a substance is cooled.

Science; States of matter; KS3 Year 7; Heating and cooling curves

1.	When a substance is cooled the temperature will fall.
2.	During condensing and freezing, energy is given out as the forces between particles gets stronger.
3.	Temperature will not fall during condensing and freezing until all of the substance has changed state.
4.	The flat line at the lower temperature represents the melting point of the solid and at the higher temperature represents the boiling point of the liquid.

Example

The temperature of a substance is decreasing, what type of curve should be used when considering the energy changes during a state change?

A cooling curve, the temperature is falling so condensation and freezing should be considered.