4.3.3.2 Pressure in Gases (physics only)

Question 1

What can happen to a gas by pressure changes?

Answer 1

• a gas can be compressed or expanded by pressure changes
• the pressure produces a net force at right angles to the wall of the gas container (or any surface)

Question 2

How is gas pressure affected when volume decreases (temp constant)?

Answer 2

• decreasing volume
• smaller distance between gas molecules and walls of container
• more frequent collisions between gas molecules and the walls/surface of the container/container wall
• each collision exerts a force on the walls of the container/side
• collisions exert more force on walls of container
• there is a greater force per unit area
• so there is a greater pressure (as pressure is force exerted per unit area)

Question 3

How is gas pressure affected when volume increases (temp constant)?

Answer 3

• increasing volume
• greater distance between particles and walls of container
• less frequent collisions on the surface of the container/container walls
• (each collision exerts a smaller force on the walls on the container/sides)
• collisions exert smaller force on walls
• smaller force per unit area
• smaller pressure (as pressure is force exerted per unit area)

Question 4

Boyle’s Law:

Answer 4

Boyle’s law states that for a fixed mass of gas held at constant temperature the product of the gas pressure and the volume occupied by the gas is equal to a constant

Question 5

Graph showing relationship of pressure and volume:

Answer 5

Question 6

What is the relationship between pressure and volume?

Answer 6

• gas pressure and volume are inversely proportional (if temp remains constant)

Question 7

When is the formula pV = constant true?

Answer 7

when the temperature is kept constant

Question 8

Equation that relates to Boyle’s Law:

Answer 8

For a fixed mass of gas held at a constant temperature:

• pressure x volume = constant
• pV = constant
• pressure = 1/volume (say constant is 1)
• pressure = constant x 1/volume
• y = m x 𝑥 + c
• has no ‘c’ as ‘c’ is 0 due to pressure being directly proportional to 1/volume meaning it has a straight line that goes through the origin
• pressure = constant/volume
• pressure x volume = constant
• p1V1 = p2V2

Question 9

How could you use data to show that pressure and volume are inversely proportional?

Answer 9

• measure pressure of gas by volume it occupies
• choose new volume and multiply new volume by new pressure
• product of second pressure and volume should be the same as the product of the first pressure and volume