Question

one difference between gas and vapour

Answer 1

The word vapor in its natural state is a solid or liquid at room temperature. However, a gas in its natural state at room temperature would still be a gas. Example: 1) steam would be a vapor because at room temperature, it would be water, which is a liquid. 2) Nitrogen (a gas) at room temperature would still be in a gaseous state.

To make it more simple, a vapor is a substance which has experienced a phase change. Whereas, a gas is a substance which has not, and will not experience a phase change.

Gas is a state of matter while vapor is not.

A gas is a substance above its critical temperature but below its critical pressure, while a vapor is a substance above its boiling point temperature.

A vapor is a gas. To me, the word, "vapor" suggests a gas that was formed by evaporation of something that is a liquid at room temperature. For example, water vapor. It also connotes a gas that can be seen.


So hen a gas condenses to liquid, two physical processes are possible. In one, the phase change occurs via nucleation and growth- small liquid drops spontaneously form and evaporate, but if a drop is larger than some critical radius, it will continue to grow ('nucleates'). This is the most common phenomenon of a gas-liquid (or liquid-solid) phase transition. Less common is 'spinoidal decomposition', which leads to coexistence of a gas and liquid phase- critical opalescence. I don't know if a spinoidal decomposition can occur in the liquid-solid transition.



SO

Gas is one of the 4 states of matter which are solid, liquid, gas and plasma, vapor does not classify as such. It is just a substance it is gaseous form.
Vapor can turn back and forth into liquid and solid states but a gas cannot
Gases cannot be see while vapors are visible
Vapors settle down on ground while gases do not

Answer 2

gas does not contain water molecules
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vapour contains water molecules