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The kinetic theory of gases assumptions is a theory based on a simplified molecular or particle description of a gas, from which many gross gas properties can be derived. It is a theory that claims that particles in a gas move freely and quickly along straight lines but often collide, resulting in changes in their speed and direction.
The pressure can also arise from the impact of these particles on the vessel walls. The greater the density of the gas, the greater the number of collisions between the molecules and the surface, and the greater the pressure exerted.
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Key Terms: Kinetic Theory, Gas, Molecules, Temperature, Boyle’s Law, Volume, Pressure, Particles
What is Kinetic Theory Of Gases?
[Click Here for Previous Year Questions]James Clark Maxwell, Rudolph, and Clausius developed the kinetic theory of gases to explain the behavior of gases.
- The theory explains the gas as a collection of small, hard spheres interacting with each other and the wall surface.
- The spheres represent gas molecules and behave according to the laws of motion.
- It describes how molecules affect gas properties such as temperature and pressure. It also explains why gases obey Boyle's Law.
- When the volume of a certain amount of gas is reduced, or when more gas is pumped into the container, the pressure increases.
- The speed of the molecules increases as the temperature of the gas increases, causing both the number and the momentum imparted by each collision to increase.
- This leads to an increase in gas pressure with increasing temperature.
The kinetic theory of gases explains the macroscopic properties of gases and the formula derived from them, the properties being volume, pressure and temperature. In low temperature, pressure, volume and temperature can be expressed in terms of:
| PV = nRT |
Where,
- n = number of moles in the gas
- R = gas constant of 8.314 JK-1mol-1
Now any gas that obeys this equation is called an ideal gas. Therefore, the equation is known as the ideal gas equation. However, there are certain assumptions that we take into account to describe the behaviour of an ideal gas.
Kinetic Theory of Gas Facts
There are several facts about Kinetic Theory, some of them are:
- According to kinetic theory, the pressure exerted by a gas is the result of collisions between gas molecules and the walls of the container where they exist.
- The gas temperature is related to the average speed of movement of the gas molecules.
- However, at a constant temperature, the speed of the molecules actually remains constant.
- Now, if one reduces the volume of the container, the molecules will have less distance to travel and therefore would hit the wall of the container and cause more pressure.
- If the volume of the container increases, the molecules hit the walls of the container at a lower speed, resulting in lower pressure.
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Assumptions of Kinetic Theory of Gas
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Kinetic theory of gas has various assumptions. Some of them include:
- Kinetic gas consists of a large number of identical molecules moving in random directions, separated by distances that are large compared to their size. molecules undergo perfectly elastic collisions or no energy loss between themselves and the walls of the container, but they do not interact.
- The transfer of this kinetic energy between molecules is heat. These theories approximate the properties of gases within a specific range of mathematical treatment.
- The separation between all molecules is comparably greater than the size of the molecules.
- All molecules in a kinetic gas obey the laws of motion.
- If a sample of kinetic gas is left for a sufficient time, it will eventually reach a steady state. Therefore, the density of molecules and the distribution of molecules are independent of position, distance, and time.
Postulates of The Kinetic Theory of Gases
[Click Here for Previous Year Questions]A theory related to gases based on molecular motion is known as the kinetic theory of gases. However, like any other theory, there are some postulates of the kinetic theory of gases as well. Some of them include:
- During the collision process, the molecules cannot lose any kind of kinetic energy. Therefore, it can easily be said that these mentioned precipitations are perfectly elastic.
- You can find enough space between these moving molecules, resulting in continuous movement between them.
- The molecules present in a gas are actually very small and far apart. This means that the volume occupied by a particular gas is only empty space and nothing else.
- Collision occurs between the molecules between each and with the walls of the container in which they are held. This collision is responsible for the gas pressure.
Define Kinetic Theory of Gases.Kinetic theory of gases can be defined as:
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Components of Kinetic Theory of Gas
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Following are the three main components of the kinetic theory of gas:
- When there is a collision between molecules, no energy is gained or lost.
- The occupied space of the molecules of gas in a container is negligible.
- These molecules always tend to have linear motion.
Things to Remember
- Kinetic theory of gas claims that gas particles move freely and fast along straight lines but also sometimes collide, causing changes in their speed and direction.
- At lower temperature, the equation which Pressure, Volume and Temperature gives is: PV = nRT
- After a collision between molecules, no energy is gained or lost.
- Kinetic Theory of Gases assumes that the size of molecules is extremely small as opposed to the distance between these molecules.
Previous Year Questions
- Total number of degrees of freedom of a rigid diatomic …
- If the pressure and the volume of certain quantity of ideal gas …
- To decrease the volume of a gas by 5% at constant temperature …
- For a monatomic gas, the molar-specific heat at constant pressure divided …
- If m represents the mass of each molecule of a gas and T, its absolute temperature …
- The respective speeds of five molecules are 2, 1.5, 1.6, 1.6 and 1.2kms−1 …
- The volume thermal expansion coefficient of an ideal gas …
- The heat absorbed by the …
- where a is a constant. The force acting on …
- Ratio of kinetic energy and rotational energy in the motion …
Sample Questions
Ques: What is Kinetic Gas Theory? [3 marks]
Ans: Kinetic gas theory explains the behavior of gases based on the concept that gas is composed of rapidly moving atoms or molecules.
- This theory is possible because interatomic forces between molecules are neglected in a gas. The kinetic gas theory defines a gas as a collection of small, hard spheres that interact with each other and the wall surface.
- The spheres will represent gas molecules and these molecules behave according to the laws of motion developed by Newton in the 17th century.
- These laws will describe how molecules affect gas properties such as temperature and pressure.
Ques. Who developed the kinetic theory of gases? [1 mark]
Ans: In the 19th century, scientists James Clark Maxwell, Rudolph, and Clausius developed the kinetic theory of gases to explain the behavior of gases.
Ques. Why is the kinetic theory of gases important? [1 mark]
Ans: The kinetic theory of gases explains the macroscopic properties of gases such as volume, pressure, and temperature.
Ques. What do you understand by the three main components of the kinetic theory of gases? [5 marks]
Ans: The kinetic theory of gases attempts to explain the complete properties of gases. These properties are based on the pressure, volume, temperature, etc. of the gases and are calculated taking into account the molecular composition of the gas as well as the movement of the gases.
Kinetic theory is also known as collision theory or kinetic-molecular theory. The three main components of the kinetic theory of gases are:
- Molecules move in linear and constant motion.
- No energy is lost or gained during the collision of molecules;
- The space occupied by the molecules present in the gas is almost negligible compared to the container in which they are kept.
Ques. What are the assumptions in the kinetic theory of gases? [3 marks]
Ans: There are various assumptions for the kinetic theory of gases such as:
- All gases in this theory are made up of molecules that are constantly and persistently moving in random directions.
- The separation between kinetic molecules is much wider than the size of the molecules.
- When a sample of a kinetic gas is kept in a container, the kinetic molecules of the sample exert no force on the walls of the container during collision.
- The duration of the collision between two kinetic molecules and between the molecule and the wall is considered to be very short.
Ques. What are the postulates of the kinetic theory of gases? [3 marks]
Ans: There are various postulates for the kinetic theory of gases such as:
- The ratio of space and volume to kinetic molecules is negligible.
- At normal temperature and pressure, there is no attractive force between kinetic molecules. So the attractive force between the kinetic molecules increases as the temperature decreases and the pressure increases.
- There is generally a lot of space between the molecules, resulting in continuous motion.
- The free movement of kinetic molecules results in a perfectly elastic collision.
Ques: At lower temperatures, give the equation for Pressure, Volume and Temperature. [1 mark]
Ans: At lower temperature, the equation that Pressure, Volume and Temperature follows is: PV = nRT
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