This tag is for questions relating to "gas", one of the four fundamental states of matter (the others being solid, liquid, and plasma). Gases follow certain laws known as the gas laws. These laws tell us about the behavior of gases i.e., the values and relations of temperature, pressure and volume etc.

A gas, made up of many particles called molecules that are in continuous random motion, colliding with one another and with the walls of the container.

Gases are complicated. They're full of billions and billions of energetic gas molecules that can collide and possibly interact with each other. Since it's hard to exactly describe a real gas, people created the concept of an Ideal gas as an approximation that helps us model and predict the behavior of real gases.

Quantitative experiments have shown that the pressure, volume and temperature of a fixed amount of gas are related by fairly simple laws. For example, for a fixed mass of gas at a constant temperature, the pressure and volume are inversely proportional to each other.

Such relations are only followed by gases at high temperatures and low pressures, far from the conditions under which they condense to a liquid. Room temperature and atmospheric pressure is sufficient for many gases. It is useful, however, to define an ideal gas as one that would follow such laws at all temperatures and pressures.

On a molecular level, such a gas would have the following properties:

  • the gas particles occupy a negligible fraction of the total volume
  • there is no long range attraction between the particles
  • all collisions are elastic

References:

https://en.wikipedia.org/wiki/Gas