Tuesday, November 22, 2011

5.18

5.17 Demo
Cloud formation
· Place a little water in the bottom of a 1½ litre plastic bottle
· Squeeze a few times
· Introduce a small amount of smoke
· Squeeze and release several times
· When you squeeze, the cloud disappears; when you release, the cloud reforms

Explanation
· When the pressure increases the temperature increases and vica versa
· The smoke particles are nucleating sites on which the water can condense

5.18 Gay-lussac's law

· 5.18 use the relationship between the pressure and Kelvin temperature of a fixed mass of gas at constant volume:

p1 / T1 = p2 / T2

p1 = Pressure at the beginning [kPa, bar or atm ]

T1 = Absolute temperature at the beginning [K]

p2 = Pressure at the end [kPa, bar or atm]

T2 = Absolute temperature at the end [K]

(Note: the units of temperature must be Kelvin, not oC! The units of pressure can be any, as long as the same at the beginning and the end)


5.18 Ideal graph and conclusion

5.18 Question


Collins, p.116


a. If we cool the gas in a rigid, sealed tin can, what happens to the pressure inside the can? (1 mark)
The pressure decreases.
b. Explain your answer to part a. by using the Kinetic Theory (4 marks)
The decrease in temperature results to the decrease in the average kinetic energy of the particles. This results to the decrease in the speed of the particles so they collide with less force and less frequently on the walls of the container. There is less force exerting on the wall resulting to the decrease in pressure.

+ The volume remains the same throughout since the tin can is a rigid container.

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