Thermal Physics

Question 1

What is the internal energy of a system?

Answer 1

The internal energy of a system is the sum of the kinetic and potential energies of all its particles

Question 2

What is true about the internal energy in ideal gases?

Answer 2

As the attractive forces between particles are negligible, the potential energy is 0, therefore the internal energy of an ideal gas is the sum of the kinetic energy of the particles

Question 3

At absolute zero what happens to the internal energy?

Answer 3

The internal energy is a minimum

Question 4

What is the kinetic energy of one mole of an ideal gas?

Answer 4

KE = 3RT/2

Question 5

What is the equation for the total kinetic energy/internal energy of an ideal gas?

Answer 5

U = 3nRT/2

Question 6

What is the internal energy of an ideal gas proportional and dependent on?

Answer 6

The internal energy of an ideal gas is proportional and only dependant on temperature

Question 7

What is heating?

Answer 7

The process of which energy transfers from one body at a higher temperature to another body at a lower temperature

Question 8

What is the zeroth law of thermodynamics?

Answer 8

If body A and body B are in thermal equilibrium with body C, then they must be in thermal equilibrium with each other.

Question 9

What is the first law of thermodynamics?

Answer 9

Q = ΔU + W

Where:
Q = the amount of heat energy supplied to/from the system
ΔU = Increase/Decrease in the internal energy of the system
W = Work done by the system as it expands or work done on the system as it contracts

Question 10

What does the first law of thermodynamics summarise?

Answer 10

Heat and work are both forms of energy and that energy is conserved

Question 11

How is work done by the gas when it expands in an ideal gas?

Answer 11

The pressure of the gas must exert a force on the container walls causing them to move outwards therefore:

Work done = FΔx
= PΔv
As pressure is the force per metre^2

Question 12

In a pV graph how is work done found?

Answer 12

The work done on the gas is the area under the graph

Question 13

What is the specific heat capacity?

Answer 13

The specific heat capacity is the amount of energy needed to raise the temperature of 1kg of the substance by 1K

Question 14

What are the units of specific heat capacity?

Answer 14

J/Kg/K

Question 15

What is the specific heat capacity equation?

Answer 15

Q = mCΔT

Q = energy
m = mass
C = specific heat capacity
ΔT = Temperature change

Question 16

What does it mean to have a high specific heat capacity?

Answer 16

Having a high specific heat capacity means that the substance doesn’t lose or gain heat energy quickly

Question 17

For an ideal gas why is it a valid assumption that PE = 0?

Answer 17

As there are no attractive forces between molecules

Question 18

What is temperature?

Answer 18

Temperature is the measure of the average kinetic energy for each molecule

Question 19

What is thermal energy?

Answer 19

Thermal energy is the kinetic energy of all the molecules in a system added together

Question 20

If a container is perfectly insulated what does it mean?

Answer 20

Heat transfer = 0

Question 21

If a container is rigid what does it mean?

Answer 21

Work done = 0

Question 22

If temperature is constant what does it mean?

Answer 22

There is no change in internal energy