Heating and Cooling Curves

Heating or cooling a substance leads to temperature changes, followed by phase changes.

Heating a substance increases its molecules' thermal energy, which is reflected as a rise in temperature until it reaches a transition point.

When the substance has absorbed enough heat, the attractive forces between its molecules are overcome, leading to a phase transition at a constant temperature.

Once the transition is complete, heating results in a rise in temperature again.

When heat is removed from the substance, the decrease in its molecules’ thermal energy corresponds to a drop in temperature, until it reaches a transition point.

Then, the temperature remains constant as stronger intermolecular forces are re-established during the phase change.

The behavior of a substance in response to temperature changes can be modeled using heating curves or cooling curves, where the temperature change is plotted as a function of the heat added or heat removed.

Consider a beaker filled with ice cubes, initially at −20 °C. As heat flows in, the temperature of the ice rises steadily. The amount of heat absorbed in warming the ice depends on the specific heat capacity of ice.

Once the melting point of i