Thermal physics

Question 1

What is the kinetic theory?

Answer 1

When energy is supplied to an object, the particles in that object take up the energy as kinetic energy and move faster.

Question 2

Explain how temperature rises?

Answer 2

The average kinetic energy of the molecules of a substance increases, then it’s at a higher temperature.

Question 3

Will a ball flying through air have temperature due to it’s motion?

Answer 3

No, the internal kinetic energy on the scale of the particles that make up an object is separate from the idea of overall movement of the object.

Question 4

How is the term molecule used?

Answer 4

Although it is a combination of atoms in Chem, any small particle is referred to as a molecule.

Question 5

At what point is temperature said to be absolute zero?

Answer 5

Taking energy away from molecules until all internal kinetic energy has been removed. The molecules will no longer be moving at this point.

Question 6

Explain heat transfer.

Answer 6

In hotter parts of a substance, molecules move more quickly(more frequent collisions, more exchange of energy)

When a high energy molecule collides with one of less, they share energy.

The heat is passed from hotter areas to colder areas.

Question 7

What does the effect of transferred heat have on temperature depend on?

Answer 7

1. The amount of heat transferred.
2. The mass of the object
3. The specific heat capacity of the material.

Question 8

What is specific heat capacity?

Answer 8

The amount of energy needed to raise the temperature of 1kg of a substance by 1K.

Question 9

Why do different things have different specific heat capacities?

Answer 9

Because their molecular structures are different.

Question 10

Which expression relates energy and temperature?

Answer 10

(change)Energy=mc(change)Temperature

Question 11

How do you measure the internal energy of a substance?

Answer 11

By summing up all the kinetic and potential(due to bonds between molecules) energies of the molecules

Question 12

Do all molecules of a substance have the same energy?

Answer 12

No, the internal energy is randomly distributed across all the molecules according to the “Maxwell-Boltzman” distribution.

Question 13

What should you know about the characteristic MBD?

Answer 13

1. There are no molecules with zero energy.
2. Only a few molecules have high energy.
3. There is no maximum value for the energy a molecule can have.
   * This distribution graph is for one specific temperature, the peak on the graph moves towards higher energies as temperature increases.

Question 14

What are the two different average speeds of particles in a material which are of interest to physicists?

Answer 14

1. Most probable speed of the particle- corresponds to the peak of the MBD graph.
2. Root mean square speed- associated with average kinetic energy.

Question 15

How is the rms speed found?

Answer 15

Squaring the individual speeds of a set of molecules.

Finding the mean of the squares.

Taking the square root.

Question 16

What is the relationship between the average kinetic energy of any molecule and the absolute temperature of the gas?

Answer 16

3/2kT is equal to the average kinetic energy of a molecule.

This shows that zero on the absolute scale must indicate a situation where the molecules are stationary.

Question 17

State Boyle’s law.

Answer 17

For a constant mass of gas at a constant temperature,

The pressure exerted by the gas is inversely proportional to the volume it occupies.

Question 18

State Charles’ law.

Answer 18

For a constant mass of gas at a constant pressure,

The volume occupied by the gas is proportional to it’s absolute temperature.

Question 19

State the pressure law(Gay-Lussac law)

Answer 19

For a constant mass of gas at a constant volume,

The pressure exerted by the gas is proportional to its absolute temperature.

Question 20

Why are the 3 gas laws idealized?

Answer 20

The law aren’t perfectly accurate,

Charles’ law states that if we reduce the temperature to zero Kelvin, the gas would have zero volume.

So we have to find a gas which did not suffer from the real world difficulties.

Question 21

What are the properties of an ideal gas?

Answer 21

1. Molecules have zero size.
2. Molecules are identical.
3. Molecules collide with each other and the walls of their containers without any loss of energy, in collisions which take zero time.
4. The molecules exert no forces on each other, except during collisions.
5. There are enough molecules so that stats can be applied.

Question 22

What is the equation of state for an ideal gas?

Answer 22

pV=NkT

Number of molecules

Question 23

What is the alternative to the equation of state?

Answer 23

pV=nRT

number of moles and R=8.31Jmol-1K-1

Question 24

What is the mole?

Answer 24

mol is an SI unit to measure the amount of a substance.

1 mol consists of the Avogadro number of molecules of that substance (6.02*10^23)