What is the difference between Gas and Vapour?

The difference between gas and vapours is that Gas is in gaseous at room temperature but vapours are liquid at room temperature.

Gas and vapor are commonly used as synonyms. However, a vapor is a specific type of gas. A vapor is a gas whose molecules gained energy and vaporized from a substance who at room temperature is either a solid or liquid. An example is water. Water is a liquid at room temperature, so when it becomes a gas it is referred to as water vapor.
 

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.

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.