Gas vs Vapor
Difference between Gas and Vapor has always been a point of discussion between people, and at the end of the debate, people find that there is not much to differentiate between the two. Before moving forward, let us first se what a gas is.
All matter on earth exists either of the three states called solid, liquid or gas. Solids have fixed shape and volume, while liquids have a fixed volume but take the shape of the container in which they are placed. The example could be water that takes the shape of a glass, jug or any other container in which it is kept. Gases do not have either shape or volume. The molecules in a gas can expand to occupy any available volume as there is very little or rather nil inter molecular attraction.
Vapor does not classify as a state of matter but is rather a liquid in its gaseous form that results because of temperature and pressure being applied. Water vapor is a perfect example of vapor. If temperature remains constant and pressure is increased, water vapor can be brought back to its original form which is water. It is surprising that we do not call water vapor as water gas, but always refer to smell of helium that emanates when balloons are being filled with it as gas. Similarly while filling gasoline in a motorcycle, if there is a smell of gasoline, you call it gasoline vapor and not gasoline gas.
Some experts have suggested that a vapor is something that can be seen or smelled or something that settles down on the ground, while one cannot see a gas but can only smell it. Though this differentiation is valid to many vapors and gases, you cannot smell water vapor.
The most important thing to remember is that there is no physical or chemical difference between a vapor and a gas. These are just terms to describe a phase of a substance, and there are many overlapping between the two terms which makes precise definitions practically impossible. Gas can be taken as a broader term that encompasses vapor in its fold. Vapor is then particular types of gas. You can technically call all vapors gases, though in many situations this might seem awkward, and even weird.
Hence, vapor, though it is not a state of matter, is a substance in gaseous state that is much lower than is required to turn the substance into a gas, also called critical temperature. Vapors normally result from boiling and evaporation.
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