When the heat content of a substance increases, but it's not at its melting or boiling point, the following happens:

The temperature of the substance increases.

Here's why:

* Heat energy is directly related to the kinetic energy of molecules. The more heat energy a substance absorbs, the faster its molecules move.

* Temperature is a measure of the average kinetic energy of molecules. So, as molecules move faster, the temperature of the substance rises.

Think of it like this: Imagine heating a pot of water on the stove. As the water absorbs heat, its temperature increases until it reaches its boiling point (100°C or 212°F). Before it boils, the heat energy is going into increasing the kinetic energy of the water molecules, making them move faster.

Important Note: This assumes the substance is in a single phase (solid, liquid, or gas). If the substance is at a phase transition (like melting or boiling), the added heat energy goes into changing the state of matter, not increasing the temperature.