Pressure and particles What causes pressure in gases? The particles of a gas are constantly moving around, and when they hit any surface they create a pressure on that surface. The more often they hit a surface the higher is the pressure

Boyle’s Law This law is about what happens to the pressure of a gas when the volume of a container changes and the temperature of the gas remains constant The pressure depends on how often the particles hit the walls of the container The more often, the higher the pressure, the less often the lower the pressure

volume is inversely proportional to pressure Double the volume > halve the pressure Halve the volume > double the pressure volume is inversely proportional to pressure Finishing Pressure = 1 Finishing Volume = 8 Starting Pressure = 2 Volume = 4 Finishing Pressure = 4 Volume = 2 Double volume Starting volume Halve volume

P1 x V1 = P2 x V2 What is the value of P x V for each result? Results table Starting Pressure P1 Volume V1 P1 x V1 Finishing Pressure P2 Finishing V2 P2 x V2 2 4 8 1 What is the value of P x V for each result? Answer = 8 so:- P1 x V1 = P2 x V2

The formula P1 x V1 = P2 x V2 is used to work out questions on Boyle’s Law. P1 = starting pressure P2 = finishing pressure V1 = starting volume V2 = finishing volume Always start off the answer by writing down: P1 x V1 = P2 x V2

A cycle pump contains 50 cm3 of air at a pressure of 100N/cm2 A cycle pump contains 50 cm3 of air at a pressure of 100N/cm2. Find its pressure if its compressed to 10cm2. P1 x V1 = P2 x V2 100 x 50 = P2 x 10 5000 = P2 x 10 P2 = 5000 = 500 N/cm2 10

A mass of gas at a pressure of 20 Pa has a volume of 3m3 A mass of gas at a pressure of 20 Pa has a volume of 3m3. What will be the volume if the pressure is doubled? P1 x V1 = P2 x V2 20 x 3 = 40 x V2 60 = 40 x V2 V2 = 60 = 1.5 m3 40

A balloon contains 8 litres of air at a pressure of 5 Pa A balloon contains 8 litres of air at a pressure of 5 Pa. What is the new pressure of the balloon if its volume is decreased to 5 litres? P1 x V1 = P2 x V2 5 x 8 = P2 x 5 40 = 5 x V2 V2 = 40 = 8 Pa 5

100m3 of air is at a pressure of 75N/m2 100m3 of air is at a pressure of 75N/m2. If the volume of air is reduced to 30m3, what is the new pressure? P1 x V1 = P2 x V2 75 x 100 = P2 x 30 7500 = P2 x 30 P2 = 7500 = 250 N/m 2 30