Question

What happens when the temperature of a substance decreases significantly?

Answer 1

Answer:

When the temperature of the substance changes the randomness and thermal motion on atomic level also changes accordingly.

That means lower the temperature means lower the motion of molecules, some times at particular temperature the phase change also occurs.

When the substance changes its phase, the energy within the substance also changes  

Also when substance change its phase the size of molecules also changes, which decreases the heat energy.

Answer 2

When temperature decreases the atoms(or molecules) within the substance begin to slow down.