Question

When water vapor is cooled, it re-forms into water droplets. Why does this represent a conservation in mass?

Answer 1

It represents a conservation in mass because the actual mass of water isn’t changing. The relationship between the molecules and the density of the water is. There is still the same amount of mass.

Answer 2

Explanation:

According to the conservation of mass, mass can neither be created nor it can be destroyed. But it can only be changed from one form to another.

For example, $H_{2}O(l) \rightleftharpoons H_{2}O(g)$

During this change only state of water is changing from liquid to gas and gas to liquid and no change in mass is taking place.

As mass of liquid water = (2 + 16) g/mol = 18 g/mol

Mass of water vapor = (2 + 16) g/mol = 18 g/mol

Hence, this shows that when water vapors are cooled then it changes into liquid state of water without causing any change in mass as mass is conserved.