Definition of Gas Laws (from Boyle, Charles, and Combined)

Boyle's Law

The first one is the Law of Boyle that establishes the relation between volume and pressure of a gas. In this case, it is known that the relationship between both variables is inversely proportional: if the pressure of a gas increases, its volume decreases proportionally. Similarly, if the pressure decreases, its volume increases proportionally. And it is also true that: if the volume increases, the pressure decreases proportionally and vice versa.

To do this, Boyle studied the behavior of gas in a "U" tube filled with Mercury, with one end open and the other closed. When Mercury is added above the level of the closed end, the volume of the

air trapped at that end decreases proportionally to the mercury addition that exerts pressure on it at the other end.

And Boyle not only observed the trend, but quantified those variations, discovering that, for example, if a a gas is compressed by reducing its volume by half, the pressure will be increased to twice the initial.

Therefore, we can express the above as follows:

P_i. V_i = P_F. V_F

Where "i" refers to the initial state and "f" to the final state.

It should be noted that Boyle studied this behavior in gases locked up to temperature constant, that is, isothermally.

Charles Law

Charles's Law came to define the relationship between two other variables, the temperature and the volume of a gas. In this way, Charles found the proportionality direct that exists between the temperature and the volume of a fixed quantity of a gas, if this is at constant pressure, that is to say, isobarically.

Let's go back to an example with Mercury. Let's suppose a tube that has a bulb at one end and is open to the atmosphere at the other end, in this way, a mercury plug can move inside it. Now, the gas pressure inside the bulb is always equal to atmospheric and the displacement The mercury plug will indicate the increase or decrease in gas volume as the gas is heated or cooled.

Let's see a homemade example, suppose you have an inflated balloon and it is exposed to a decrease in temperature, we will see that the balloon automatically begins to decrease in volume. When the balloon is returned to temperature environment, again the temperature rises and the balloon expands. Therefore, the directly proportional relationship that exists between temperature and volume is demonstrated. In this case, when the balloon heats up, the temperature of the particles inside increases and the Kinetic energy of them also does. This produces an increase in strength They exert on the walls of the balloon and the balloon expands without increasing the internal pressure beyond the initial pressure.

Therefore, Charles points out that the volume of any gas is directly proportional to its temperature in degrees Kelvin if the pressure is kept constant.

Combined gas law

Recapitulating, it is known that the volume of a gas is inversely proportional to its pressure and directly proportional to temperature. However, Charles and Boyle studied these behaviors by keeping some of the variables constant. Because of this, it is considered equally valid to determine one of the three variables regardless of the order in which the other two vary. That is, you can first estimate the volume of a gas from a pressure change and then from a temperature change, or vice versa.

This implies that, when pressure and temperature change in a gas, both laws can be used in a way independent and furthermore, the volume of a gas at constant temperature and pressure is directly proportional to the number of gas particles.

Topics in Gas Laws (from Boyle, Charles, and Combined)