Thermal Physics

Question 1

What is internal energy?

Answer 1

The sum of the potential and kinetic energies of a system.

Question 2

How can you increase the thermal energy of a system?

Answer 2

We can increase it by heating it up or doing work on the object.

Question 3

Explain the energy changes that occur during a change of state.

Answer 3

During change of state the potential energy of the particles change but the kinetic energies don’t change.

Question 4

What equation can be used to determine the energy required to change the temperature of a substance?

Answer 4

Q = mcΔt

Question 5

Give the equation to work out the energy for change of state?

Answer 5

Q = ml

Question 6

What is the ideal gas equation?

Answer 6

pV = nRT

Question 7

What is the first law of thermodynamics?

Answer 7

ΔU = Q - W

Question 8

What is the specific heat capacity of a substance?

Answer 8

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

Question 9

What is the specific latent heat of a substance?

Answer 9

The energy required to change the state per unit mass of a substance, while keeping the temperature constant.

Question 10

What is an ideal gas?

Answer 10

A gas that:
- the gas molecules don’t interact with each other
- the molecules are thought to be perfect spheres.

Question 11

What is the internal energy of an ideal gas equal to?

Answer 11

It is equal to the sum of kinetic energies of all its particles.

Question 12

What is Boyle’s law?

Answer 12

Pressure is inversely proportional to volume providing temperature is constant.

Question 13

In an ideal gas, how would increasing the volume change the temperature of the gas, while the pressure remains constant?

Answer 13

As you increase the volume, you also increase the temperature.

Question 14

Explain how increasing the temperature of a balloon, while keeping the volume the same will increase the pressure.

Answer 14

• as temperature increases, the average Ek increases
• therefore the particles are travelling at a higher speed on average
• there are also more frequent collisions
• which means the particles would exert a greater force
• which would cause an increased rate of rate of change of momentum
• therefore increasing pressure

Question 15

What is absolute zero?

Answer 15

At -273 degrees celcius
Where objects have no Ek

Question 16

What is avogadro’s constant?

Answer 16

The no. of atoms there are in one mole of a substance.

Question 17

True of false: ‘All collisions between particles and the wall are elastic’ is an assumption of an ideal gas?

Answer 17

True

Question 18

State an assumption of an ideal gas related to time.

Answer 18

The time for each collisions is negligible in comparisn to the time take between collisions.

Question 19

Describe 3 other assumptions of the ideal gas equation.

Answer 19

• the particles move randomly
• they follow newton’s laws of motion
• no intermolecular forces act between particles
• volume of the particles is negligible compared to the volume of the container they are in.

Question 20

What is meant by the root mean square speed?

Answer 20

The square root of the mean of the squares of the speeds of the molecules.

Question 21

What is Brownian motion?

Answer 21

Brownian motion is the idea that very small objects have random motion in a liquid or gas due to random bombardment by the molecules in this substance. This movement will be fractionally more on one side than the other so a force will push it for an instant as the net forces shifts directions. This random motion is Brownian motion and gives evidence for the existence of atoms.