Gases and Kinetic Theory COPY

Question 1

What was used to see Brownian motion?

Answer 1

Smoke particles with a microscope

Question 2

What is Brownian motion?

Answer 2

Where particles seem to be wriggling unpredictably.

Question 3

How did Brownian motion show the existanceof molecules and atoms?

Answer 3

The unpredictable wriggling is due to being bombarded unevenly and experiences forces due to these impacts, which changes its magnitude and direction.

Question 4

What is pressure caused by?

Answer 4

The molecules in a gas bombarding the walls of the container

Question 5

What does the graph of pressure against temperature look like?

Answer 5

Question 6

Define absolute zero

Answer 6

The temperature where the pressure of an ideal gas becomes 0

Question 7

Draw the graph of pressure against volume

Answer 7

Question 8

Draw the graph of pressure against 1/volume

Answer 8

Question 9

How would you use an experiment showing Boyle’s Law to show that P is directly proportional to 1/V

Answer 9

Question 10

What is Boyle’s Law?

Answer 10

P is directly proportional to 1/V

Question 11

How would you use an experiment showing Charles’s Law to that volume is proportional to temperature

Answer 11

Question 12

What is Charles’s Law?

Answer 12

V is directly proportional to T

Question 13

Explain how the experiment showing the pressure Law and be. used to prove P is directly proportional to T

Answer 13

Question 14

what does the pressure law show?

Answer 14

P is directly proportional to T

Question 15

What is the molar mass?

Answer 15

The mass of one mole of a gas (Mr)

Question 16

What is the molecular mass?

Answer 16

The mass of one molecule of the gas

Question 17

Define mole

Answer 17

The number of atoms of C-12 in 12g of C-12

Question 18

What are the three gas equations (moles)?

Answer 18

mass = mr x mol

N = N_a x mass / mr

mol = N / N_a

N = No. of molecules

N_a = Avagadro’s Constant

Question 19

What are the three arrangements of the ideal gas equation?

Answer 19

pV = nRT

P₁V₁ / T₁ = P₂V₂ / T₂

pV = NkT

Question 20

Define an ideal gas

Answer 20

One which obeys the equation pV = nRT at all temperatures and pressures

Question 21

What are real gases

Answer 21

Gases that behave like ideal gases at low pressures and temperatures above room temperatures

Question 22

When does an expanding gas do no work?

Answer 22

When it is expanding into a vacuum

Question 23

What is the equation for the work done by an expanding gas at constant temperature?

Answer 23

W = p∆V

Question 24

Why does a gas exert a force on a wall?

Answer 24

• The gas molecules collide elastically with the walls of the container
• Their velocity will change direction but keep the same magnitude
• This causes the component of their momentum perpendicular to the wall to change
• By Newton’s second law the molecules must have a resultant force on them to cause this change in momentum
• This resultant force is exerted by the wall on the molecules
• By Newton’s third law, if the wall puts a force on the molecules, the molecules must put an equal opposite force on the wall
• The forces from all the molecules cause a pressure on the wall, which can be calculated by P = F / A

Question 25

Why does increasing the temperature of the gas increase the pressure?

Answer 25

• Average kinetic energy increases
• Higher average speed
• Greater rate of change of momentum when hits wall so a greater force and so greater pressure
• They also hit the wall more times per second

Question 26

Why does decreasing the volume of a gas increase the pressure?

Answer 26

• More collisions with the container per second
• Rate of change of momentum of the particles hitting the wall will increase
• The force on the wall will increase
• So pressure will increase as pressure = F / A

Question 27

Find the rms speed of molecules with speeds of 100,200,300,400,500 ms-1

Answer 27

rms = 331.6 ms-1

(100² + 200² + 300² + 400² + 500²) /6

Question 28

How do we assume the molecules behave in an ideal gas?

Answer 28

• Number of molecules is very large
• Molecules are in random motion
• Forces between the gas molecules are negligible until they collide
• The collisions between the molecules and the walls are perfectly elastic
• The volume of the molecules is negligible compared to the volume of the container
• The duration of the collisions between molecules and the walls of the container and each other is negligible compared to the time between collisions

Question 29

Describe what random motion is

Answer 29

• They have a range of speeds
• The motion of a molecule changes unpredictably
• They have no preferred direction of motion

Question 30

What is a perfectly elastic collision?

Answer 30

A collision where they lose no kinetic energy when they collide

Question 31

Derive the formula for the force on the wall exerted by one molecule of gas.

Answer 31

Question 32

Derive the formula for kinetic theory (pressure exerted by N molecules)

Answer 32

Question 33

Derive 1/2mc² = 3/2kT

Answer 33

Question 34

If you have hydrogen gas and oxygen gas at the same temperature, why does hydrogen have a huger C_rms

Answer 34

The average kinetic energy will be the same, but the hydrogen has a lower mass so it will have a greater C_rms

Question 35

What will happen to the C_rms if the temperature of an ideal gas is doubled

Answer 35

x √2

Question 36

Prove that the C_rms is directly proportional to the square root of the temperature.

Answer 36

Question 37

Derive the equation for pV = NkT

Answer 37