(a) Explain, by the molecular model,
(i) how the air inside a cylinder exerts a pressure on walls of the cylinder.
(ii) why the pressure in a cylinder increases as the cylinder gets heated
(iii) why the pressure in a cylinder increases as more air is pumped into the cylinder.
(iv) what happens to a block of ice when the temperature of ice is increased and the ice does not melt.
(b)The diagram shows a box with a partition which can be raised. The two parts of the box are filled with two different gases, gas A and gas B.
A long time after the partition has been raised, the gases are found to be completely mixed. Explain how this happened and why it takes a long time.
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Answer:
(a)
(i) The air molecules collide with the inner walls of the cylinder and so air molecules exert a force on the walls. Since force is the product of pressure and area, the air molecules exert pressure on the walls when they exert a force on them.
(ii) As the temperature of the air increases, the average kinetic energy of the air molecules increases. This increases the frequency of collision between air molecules and the walls of the cylinder, causing the pressure to increase.
(iii) As the number of air molecules in the cylinder increases, the average separation between air molecules decreaes. This increases the frequency of collision between the air molecules and the walls of the cylinder, hence causing the pressure to increase.
(iv) The molecules in the ice vibrate with more energy but there is no change in the pattern of arrangement of the molecules.
(b) The unrestricted random continuous motion of gas molecules allows them to penertrate into the large spaces between molecules and mixing of gases takes place, As there are many gas molecules in the jar, the collisions with other gas molecules make the diffusion process slow.
