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What is Vacuum?

Vacuum is produced by removing gas from a container. It is not possible to remove all the gas from a container by pumping; particles still remain in the container, producing a pressure. Zero pressure is therefore not possible in practice. The pressure relative to the absolute vacuum is called the absolute pressure. Thus there is still a positive pressure even in a good vacuum.

What is Partial Pressure?

Partial pressure is produced by a single gas in a mixture of gases. The table below shows the percentage composition of air. At a pressure of 1.013 bar the oxygen content is 21.224%, the partial pressure of oxygen in air is = 0.21224 bar or 212.24 mbar.

What is Gas?

Gas is a substance, where the particles (molecules and atoms) can freely move. In thermodynamic equilibrium these particles are uniformly distributed in space, so that the pressure, partial pressures and gas composition are the same at all points of the container. A solid is a substance, the particles are fixed in their positions, they can only vibrate and rotate.

What is Vapour Pressure?

When the pressure above a liquid is reduced at constant temperature, it evaporates and the resulting gas is called a vapour. This vapour, like other gases, has a pressure called vapour pressure. The vapour can become a liquid again. This is called condensation. All vapours have a saturation pressure which is the pressure of the vapour in equilibrium with its liquid.

What is mean free path?

The mean free path (MFP) is the average distance which a molecule of a gas- or vapour travels before it collides with another molecule. At high vacuum, these distances become very large, so the particles collide only with the walls of the vacuum chamber.