question_answer

A gas is filled in a cylinder fitted with piston at a constant temperature. Explain on the basis of kinetic theory: (i) The pressure of the gas increases by raising the temperature. (ii) On pulling the piston out, the pressure of the gas decreases.

Answer:

                (i) On raising the temperature, the average speed of the gas molecules increases. As a result, the molecule collide more frequently with the walls of the vessel and also greater momentum is transferred to the wall in each collision. Both of these factors increase the pressure of the gas. (ii) When the piston is pulled out, the volume of the gas increases. The molecules have to traverse a large distance to collide with the walls of the cylinder. So a lesser number of molecules collides with the walls per second. Moreover, the collisions now occur on a larger area of the walls. Both of these factors decrease the pressure of the gas.