NEET Physics Notes Mechanics-Behaviour of Perfect Gas and Kinetic Theory Equation of State of a Perfect Gas
Equation of State of a Perfect Gas
Equation of State of a Perfect Gas
The gas whose molecules are point masses i.e. do not possess volume and do not attract each other are called ideal or perfect gas. It is a hypothetical concept which does not exist in reality.
Important Points Regarding a Perfect Gas
- An actual gas or real gas such as hydrogen or oxygen or helium, behaves as ideal gas most closely at low pressure and high temperature.
- The equation pV = RT is called perfect gas equation for one mole of a gas R is universal gas constant. The SI unit of gas constant is J/mol-K. Its value is 8.314 J/mol-Ktor 8.314 x 107 erg/mol-K or 2 cal/mol-K. The dimensions of R are
- Boltzmann’s constant is represented by per mole gas constant
Kinetic Theory of Gases
Kinetic theory of gases relates the macroscopic properties of gases (such as pressure, temperature etc.,) to the microscopic properties of gas molecules (such as speed, momentum, kinetic energy of molecules etc).
Different Assumptions of Kinetic Theory of Gases
- Every gas is composed of tiny particles known as molecules. The size of molecules is much smaller than the intermolecular spacing.
- The molecules of a gas are identical, spherical, rigid and perfectly elastic point masses.
- Molecules are in a state of random rapid motion. They collide with each other. There is no loss of energy during collision. Only the direction of motion is changed.
- The time spent in collision between two molecules is negligible in comparison to time between two successive collisions.
- The number of collisions per unit volume in a gas remains constant. No attractive or repulsive force, acts between gas molecules.
- Gravitational attraction among the molecules is ineffective due to extremely small masses and very high speed of molecules.
- Molecules constantly collide with the walls of container due to which their momentum changes. The change in momentum is transferred to the walls of the container. Consequently, on the walls of container pressure is exerted by gas molecules. The density of gas is constant at all points of the container.
Kinetic Energy and Temperature
