Thermal Physics

Question 1

What is the internal energy of a body

Answer 1

Internal energy, U, is the sum of the randomly distributed kinetic energies and potential energies of the particles in a body

U=Σ(kinetic energies)+Σ(potential energies)

Question 2

What is the first law of thermodynamics

Answer 2

The increase in internal energy of a system is equal to the heat added to the system minus the work done by the system

∆U=∆Q-∆W

U = increase in internal energy of the system 
Q = thermal energy added to the system 
W= work done by the system

Question 3

When will a gas do work

Answer 3

-When a gas expands, it exerts a force on the surroundings, causing them to move – the gas does work on the surroundings

Question 4

Explain what occurs when a hot liquid or solid is placed into a cold liquid

Answer 4

The internal energy transferred from the hot object when it cools down is equal to the thermal energy gained by the cold liquid and its container, plus the thermal energy lost to its surroundings

Question 5

Define specific latent heat

Answer 5

The specific latent heat of a material is the amount of thermal energy required to change the state of 1kg of material, without a change in temperature, at a specified ambient pressure

Question 6

Explain Boyles’ law

Answer 6

For a fixed mass of an ideal gas at constant temperature, the pressure of the gas Is inversely proportional to its volume

p1V1=p2V2

Question 7

Explain Amonton’s law

Answer 7

There is a linear relationship between pressure and temperature of a gas – providing that the mass and the volume of the gas are kept constant

P1/T1=P2/T2

Question 8

What is Absolute zero

Answer 8

The temperature when all molecular motion ceases, and the pressure of a gas drops to zero. The accepted value is the zero if the Kelvin temperature scale and is defined as -273 degrees Celsius. 0K=-273

Question 9

Explain Charles’ law

Answer 9

At a constant pressure the volume of a fixed mass of an ideal gas is directly proportional to its absolute temperature

V1/T1=V2/T2

Question 10

Explain Avogadro’s law

Answer 10

Equal volumes of gases at the same temperature and pressure contain the same number of molecules

Question 11

Give two ways a value for moles can be calculated

Answer 11

Moles = mass (g) / molar mass (g/mol)

Moles = Atoms/ Avrogrado’s Number

Question 12

What is the equation for Work Done

Answer 12

W= p x V

Question 13

What are the properties of an Ideal gas

Answer 13

R - random direction
A - attraction - none between particles
V - Volume: molecules/ particles have negligible volume
compared to the Volume of the gas
E - elastic collisions- EK is conserved
D - duration of collisions very short compared to time
between