Dynamics of change of pressure of gas depends on the causes of changes of this size and also on conditions under which there is an increase or reduction of pressure of gas. All these factors have the molecular nature.
What gas pressure depends on
The physical meaning of size of pressure of gas is in the intramolecular phenomena occurring in substance. It is known that particles of gas are in the continuous random motion called Brownian. Each particle on the way of the trajectory faces both other particles of gas, and walls of a vessel in which there is a gas.
The blow of molecules about walls of a vessel generates change of an impulse of a particle. From the second law of Newton it is known that change of an impulse of a material point for some period it is equivalent to action of some force causing this change or generated by change of an impulse. Determination of size of pressure means the relation of force operating on some surface to the size of the area of this surface.
Thus, blows of molecules about walls of a vessel lead to emergence of pressure as macroscopic phenomenon. From here also the possibility of change of pressure of gas follows.
Dependence of pressure on temperature
Heating or cooling of substance of gas, first of all, leads to increase or reduction of speed of the movement of its particles because the body temperature size essence consists in it. Change of speed leads to changes in differences of an impulse at blows of molecules about vessel walls that generates change of pressure of gas. However it is worth noticing that pressure in this case will change only in case the walls limiting a vessel motionless. If the volume of a vessel can change depending on external conditions, then fluctuations of temperature will not lead to changes in gas pressure.
Dependence on volume
As the macroscopic pressure of gas is caused by total number of blows about vessel walls, changing the number of blows, it is possible to change also the size of pressure. Such effect is found at change of volume of the vessel containing gas. The vessel size, the less length of a free run of particles of substance are less that leads to their more frequent collisions as with each other, and with vessel walls. As a matter of fact, an extreme case of reduction of pressure due to increase in volume of a vessel is the mental experiment on removal of walls of container with gas on infinite distances. In this case pressure of gas tends to zero.
Dependence on concentration
Concentration of particles of substance is determined by their quantity which is the share of single volume. That is it is possible to increase concentration, having increased the total number of particles of gas at a vessel volume constant. Increase in amount of atoms of gas leads to more frequent collisions and, as a result, to increase in pressure again. Therefore more rarefied gases have the smaller pressure and weight.