Explanation:

When a substance is heated, the intermolecular space between molecules increases. This is because heating a substance increases the kinetic energy of the molecules, causing them to move faster. As the molecules move faster, they collide with each other more frequently and with greater force. These collisions push the molecules apart, increasing the distance between them and therefore increasing the intermolecular space.

Key Points:
- Heating a substance increases the kinetic energy of the molecules.
- Increased kinetic energy causes molecules to move faster.
- Faster-moving molecules collide more frequently and with greater force.
- Collisions between molecules push them apart, increasing the intermolecular space.
- Therefore, the intermolecular space between molecules increases when a substance is heated.

Example:

Let's consider an example of a solid substance, such as ice, being heated to become a liquid, water.

In the solid state, the molecules in ice are tightly packed together, with relatively little intermolecular space. However, when heat is applied to the ice, the kinetic energy of the molecules increases. As a result, the molecules start to vibrate and move more rapidly.

As the molecules gain more kinetic energy, they collide with each other more frequently and with greater force. These collisions push the molecules apart, increasing the distance between them. The intermolecular space between molecules in the ice increases as the solid melts into a liquid.

This increase in intermolecular space is also evident when considering the expansion of substances upon heating. For example, when a metal rod is heated, it expands because the molecules in the rod have more kinetic energy and move further apart. This expansion occurs due to the increase in intermolecular space between the molecules.

In summary, when a substance is heated, the kinetic energy of the molecules increases, causing them to move faster and collide more frequently. These collisions push the molecules apart, increasing the intermolecular space between them. Therefore, the intermolecular space between molecules increases when a substance is heated.