Question

The density of a substance decreases when its temperature increases. Give reason.

Answer 1

1. When the temperature increases, the atoms/molecules of a substance get scattered because of a gain in energy.
   
2. The image above depicts how on increasing the temperature, particles of matter start moving faster.
3. Thus, all the substances expand on heating and contract on cooling but the mass of a substance remains unchanged.
4. As we know, $density=\frac{mass}{volume}$
5. If the volume would increase then the density would decrease as they are inversely proportional.
6. Hence, the density of a substance decreases with an increase in temperature.