What are the Gas Laws?

The gas laws came into force in the 17th century to help researchers determine quantities, amounts, pressures, and temperatures while dealing with gases. There are three main gas laws: Charles’ Law, Boyle’s Law, and Avogadro’s Law (they all collectively become General Gas Equation and Ideal Gas Law).

Gas laws

The relationship between all the quantities like pressure, temperature, volume, and amount of gas will be derived from three fundamental gas laws. Boyle’s law says that the volume of gas will rise if the pressure decreases. Charles’ law states that the volume of a gas increases as the temperature rises. Lastly, Avogadro’s Law states that as the volume of gas increases, so does the amount of gas. So, you now derive the ideal gas law using the result of combining the three basic gas laws.

Ideal Gases

The ideal gas states that the perfect gas is a theoretical substance that will help in determining the relationship between four gas variables, i.e. pressure (P), volume (V), amount of gas (n), and temperature (T). Here are some points to keep in mind. Gas also does not take much space. This ideal gas transfer moves from one place to have. It can move in only directions, which is a straight line, at random, and in a circle. Gas particles do not possess forces. Some particles will only clash elastically with one another and the container walls.

Real Gases

Real gases have real volume and involve the collision of elastic particles. It is because these attractive forces attract the particles. Because of this interaction, the volume of a real gas is much larger than that of the ideal gas. Moreover, the pressure of real gas is lower than that of an ideal gas. These gases tend to perform ideal gas behaviour because of low pressure and extremely high temperature.

The compressibility factor (Z) will tell you about how much the real gases will differ from the behaviour of ideal gas:

Z = PV / nRT gas law (1)

For ideal gases,  Z=1. For real gases,  Z≠1 

Boyle’s Law

Robert Boyle established the relationship between pressure (P) and volume (V) in 1662 (thinking that temperature (T) and gas quantity (n) will remain constant):

P ∝ 1/V → PV = x gas law (2)

Here, x would be the constant, which will vary according to the amount of gas present at a given temperature.

Pressure is inversely proportional to volume

Assuming that another form of the equation can be useful in solving problems (we can say two sets of circumstances and setting both constants to each other) is:

P1V1   = P2V2

Question: If a 17.50mL sample of gas is given containing 4.500 atm. What is the volume if the pressure is increased to 1.500 atm and the amount of gas and temperature remain constant?

V2 = P1 V1 / P2            

= 4.500 atm X 17.50 mL / 1.500 atm.            Gas law (5) 

= 52.50 ml              gas law (6) 

Charles’ Law

French physicists Jacques Charles in 1787, found the relationship between Temperature (T) and Volume (V) [assuming Pressure (P) and Amount of Gas (n) remain constant]:

V1 / T1 = V2 / T2

Here, y is a constant that depends on the amount of gas and pressure. So, volume is directly proportional to temperature. In the following equation, let us assume two sets of conditions. Setting both constants to each other will help solve problems: 

V1T2 = V2T1

Question: If a sample of Carbon dioxide in a pump has a volume of 20.5 mL at 40.0 degree Celsius. The gas and pressure remain constant, determining the new volume of Carbon dioxide in the pump if the temperature goes up to 65.0 degree Celsius.

V2 = V1. T2 / T1 

= 20.50 ml (60 + 273.15 K ) / 40 + 273.15 K

= 22.1 ml

Avogadro’s Law

Amedeo Avogadro, in 1811, corrected Gay-Lussac’s problems in determining the relationship between the amount of gas(n) and Volume(V) (assuming Temperature(T) and Pressure(P) remain constant).

V is directly proportional to n 

Here, z would be the constant that will depend on Pressure and Temperature.

• Volume(V) will be directly proportional to the amount of gas(n)

We will see there are 2 sets of conditions, and setting both constants to each other that will help solve problems is:

V1/n1 = z = V2 / n2

Conclusion

All gases behave the same when the conditions are normal. However, even minor changes in physical parameters like pressure, temperature, or volume produce a divergence. Gas laws are used to study the behaviour of gases. The state variables of a gas, such as pressure, volume, and temperature, reflect the true nature of the gas.