kinetic Theory of gasses

1. Internal energy Internal energy is the total energy contained within a system, encompassing both the kineticenergy of its molecules (due to their motion) and the potential energy due to intermolecular forces. It's a state function What happens to internal energy of a substance, when it is heated? As per Kinetic theory of gases: <K.E> ∝ T By changing temperature By doing work How can we change the internal energy of the system?

2. Sign conventions for change in internal energy: If U1 is internal energy at temperature T1 and U2 is internal energy at T2 than; ΔU= U2 – U1 Following are the conventions: If temperature of system increases than U2>U1, hence ΔU is (+) If temperature of system decreases than U1>U2, hence ΔU is (-). If temperature of system is constant than U1=U2, hence ΔU=0

3. State function: A state function is a property of a system that depends only on the current state of the system, not on the path taken to reach that state.

4. Kinetic Theory of Gases: The kinetic theory of gases was primarily presented by Daniel Bernoulli in his 1738. Bernoulli's work laid the foundation, other scientists like John Herapath, John James Waterston, and later, James Clerk Maxwell and Ludwig Boltzmann, significantly contributed to its development. • The kinetic theory of gases is a theoretical model that describes; • The molecular composition of the gas in terms of a large number of sub-microscopic particles, which include atoms and molecules. • Further, the theory explains that gas pressure arises due to particles colliding with each other and the walls of the container. • The kinetic theory of gases also defines physicalproperties such as temperature, volume and pressure. The basic version of the model describes an ideal gas. It treats the collisions as perfectly elastic and as the only interaction between the particles.

5. Kinetic Theory of Gases Postulates: The kinetic theory of gas postulates is useful in understanding the macroscopic properties from the microscopic properties. • Gases consist of a large number of tiny particles (atoms and molecules). These particles are extremely small compared to the distance between the particles. The size of the individual particle is considered negligible, and most of the volume occupied by the gas is empty space. • These molecules are in constant random motion, which results in colliding with each other and with the walls of the container. As the gas molecules collide with the walls of a container, the molecules impart some momentum to the walls. Basically, this results as pressure. • The collisions between the molecules and the walls are perfectly elastic, which means when the molecules collide, they do not lose kinetic energy. Molecules never slow down and will stay at the same speed. • The molecules do not exert any force of attraction or repulsion on one another except during collisions.

6. Ideal gas : “An ideal gas is a theoretical concept describing a gas whose molecules exhibit no intermolecular forces and have no volume.” At low pressure and high temperatures The density of gas will be low. The distance between gas molecules will be large and intermolecular forces are negligible; therefore, real gas behaves as ideal gas. At high pressure and low temperature The density of gas will be high. The distance between gas molecules will be smaller and intermolecular forces will be stronger; therefore, real gas cannot behave as ideal gas.