Kinetic Theory

Question 1

What are the assumptions made in the derivation of the kinetic theory of gasses equation?

Answer 1

• Random motion
• Elastic collisions
• Volume of particles negligible compared to volume of the container
• Time during collisions negligible to time between collisions
• No force exerted between molecules except during collisions

Question 2

When asked to explain something in terms of the kinetic theory model, what must you refer to?

Answer 2

• The rate/frequency of collisions
• The change in momentum per collision
• The total rate of change of momentum
• F=∆p/∆t and P = F/A

Question 3

What is Boyle’s Law and under which conditions is it true?

Answer 3

For a fixed mass of gas at constant temperature:

pV=constant

Question 4

What is Charles’ Law and under which conditions is it true?

Answer 4

For a fixed mass of gas at constant pressure:

V/T=constant

Question 5

What is the Pressure Law and under which conditions is it true?

Answer 5

For a fixed mass of gas at constant volume:

p/T=constant

Question 6

What is the definition of the Avogadro constant?

Answer 6

The number of atoms in 12g of carbon-12

[The number of atoms/molecules/particles in one mole of substance]

Question 7

Which two equations can be used to calculate the number of moles?

Answer 7

No. Moles= (molar mass)/(molecular mass)

No. Moles= (No. Molecules)/(Avogadro Const.)

Question 8

Which two equations are known as the ideal gas equation?

Answer 8

pV=nRT

pV=NkT

Question 9

Which equation is derived using the kinetic theory of gases?

Answer 9

pV=1/3 Nmc^2

[p=1/3 ρc^2]

Question 10

What is the equation that allows you to calculate the mean KE of a gas molecule and how is it derived?

Answer 10

pV=NkT=1/3 Nmc^2

kT=1/3 mc^2

3/2 kT=1/2 mc^2

Question 11

What is the equation that allows you to calculate the internal energy of an ideal gas?

Answer 11

3/2 NkT

Question 12

What is the equation that you to calculate the work done on/by a gas?

Answer 12

W=p∆V

Also the area under a p-V graph

Question 13

What is meant by the internal energy of substance?

Answer 13

The sum of the randomly distributed kinetic energy and potential energy of all the particles in a body

Question 14

Why is it wrong to say that the speed and kinetic energy of the molecules increase with temperature?

Answer 14

You must refer to the mean KE and the RMS speed as not all molecules will increase in speed!

Question 15

What is the definition of Specific Heat Capacity?

Answer 15

The energy needed to raise the temperature of 1kg of the material by 1°C without any change of state

Question 16

What is the definition of Specific Latent Heat of Fusion?

Answer 16

The energy required to change 1kg of a material from a solid to a liquid without a change in temperature

Question 17

What is the definition of Specific Latent Heat of Vaporisation?

Answer 17

The energy required to change 1kg of a material from a solid to a liquid without a change in temperature

Question 18

What is meant by random motion?

Answer 18

Molecules have a range of speeds and no preferred direction of movement

Question 19

What is the equation that relates to Specific Latent Heat?

Answer 19

Q=ml

Question 20

What is meant by the 1st Law of Thermodynamics?

Answer 20

The increase in internal energy = to the energy transferred by heating + work done on the system

[∆U=Q+W]

Question 21

Why is the specific latent heat of vaporisation much greater than the specific latent heat of fusion?

Answer 21

Particles move much further apart so much more work is done (against the field). Therefore there is a greater increase in potential energy.

Question 22

What is the unit of absolute temperature and how is it related to the Celsius scale?

Answer 22

The Kelvin

Kelvin Temperature = Celsius Temperature + 273

Question 23

What is the equation that relates to Specific Heat Capacity?

Answer 23

Q=mc∆θ