Summary on the kinetic molecular theory of gases

Postulates of the kinetic molecular theory of gases:

The kinetic molecular theory of gases (KMT), or simply referred to as the kinetic theory of gases, was established in the 19th century by the great works of James Clerk Maxwell (a British scientist) and Ludwig Boltzmann (an Austrian physicist) during their respective studies on gaseous behavioral pattern.

These behavioral patterns of gaseous molecules are explained in terms of pressure, temperature, viscosity, thermal conductivity and volume through their constant, random and linear motion at room temperature. Examples of gaseous molecules include oxygen (O2), chlorine (Cl2) and carbon(IV)oxide (CO2) respectively.

The postulates of the kinetic theory of gases simply refers to the basic principles of gaseous behaviours. This behavior can be properly studied when the gas particles are contained; (that is, the gas particles are present inside a sealed container). See the image below:

Meanwhile, understand that the use of a sealed or closed container is important due to the constant motion of gases at room temperature. In this regard, the gas molecules will move, diffuse and disappear into the atmosphere if not contained.

The behavioral patterns and characteristics of gas molecules are summarized in their constant random motion, particles collision, occupied volume, particles size, closeness of particles and kinetic energy generated by these particles. In this regard, the five basic postulates of the kinetic theory of gases are listed below:

1. Gas molecules move randomly in a straight line.

2. The collision between the gas molecules are perfectly elastic.

3. The actual volume occupied by each gas molecule is neglible.

4. The cohesive forces between the gas molecules are neglible.

5. The average kinetic energy of the gas molecules is directly proportional to the absolute temperature.

You can read a detailed explanation on these postulates of kinetic theory of gases here.

With regards to the kinetic theory of gases (as listed above), important facts can be deduced. These deductions have proven to be useful in our world today. As an instance, helium (He) is preferred in the filling of balloons due to its light weight (mass), unlike carbon(IV)oxide (CO2) which is heavier in mass. However, the latter (CO2) is applied in soft drinks since it is readily absorbed into the liquid (soft drinks and soda), thus forming tiny bubbles in it.

A good knowledge on the kinetic theory of gases will aid students in understanding various laws of chemistry. This include Boyle's law, Charles' law, Gay-Lussac's law of combining volumes, Dalton's law of partial pressure, Graham's law of diffusion and Avogadro's law.

From the above explanations so far, below is an overall summary on the kinetic theory of gases:

• All gases are made up of tiny molecules that are constantly, randomly and persistently moving in straight lines.

• All the molecules in an ideal gas obey Newton's laws of motion.

• The separation (distance) between the gaseous molecules are overwhelmingly greater than the size of each molecule.

• Collisions between the gas molecules themselves and the walls of the container are considered to be perfectly elastic.

• Compared to the space present inside the container, the size of the gas molecules are very small or neglible.

• If a gas sample is kept in a container, the molecules making up the gas will not exert any force on the walls of the container during collision.

• The time interval of a collision between two molecules, and between a molecule and the walls of the container is considered to be neglible.

• If a gas sample is left for a sufficient time, it will eventually come to a steady state. In this case, the density of molecules and their distributions are independent of position, distance and time.

• The average kinetic energy of the gaseous molecules is temperature dependent and will always be in proportion to it.

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