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

p1/T1=p2/T2

3/293=p2/328

p2= 3.4 bar

 

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)

As the temperature decreases, the average kinetic energy of the particles decreases. This means that they move around with less energy. This would mean that they hit the container with less force and less frequently.