Thermal Physics

Question 1

Define the concept of specific latent heat using fusion and vaporisation., and use it to explain why specific latent heat of vaporisation is always larger than specific latent heat of fusion.

Answer 1

Latent heat of fusion is heat required per unit mass to change a substance from solid to liquid phase without change in temperature.

Latent heat of vaporisation is heat required per unit mass to change a substance from liquid to gaseous phase without change in temperature.

L_f > L_v because energy is needed to increase potential energy of molecules by breaking bonds and increase separation of molecules, and to do work against atmospheric pressure.

Question 2

Describe internal energy.

Answer 2

It is determined by the state of the system, expressed as the sum of random distribution of kinetic and potential energies associated with the molecules of the system.

Question 3

What is specific heat capacity?

Answer 3

It is quantity of heat absorbed or liberated per unit mass per unit temperature change.

c = Q/mΔθ

Question 4

State the First Law of Thermodynamics.

Answer 4

The internal energy of a system is a function of its state, and increase in internal energy of a system is equal to the sum of the heat absorbed by system and work done on the system.

ΔU = q + w

Question 5

What do you understand by ideal gas?

Answer 5

In theory, ideal gas obeys equation of state pV = nRT at all pressure, volume and temperature.

Question 6

What are some assumptions for ideal gas?

Answer 6

• volume of molecules is negligible compared to total volume occupied by gas
• intermolecular forces of attraction are negligible
• collisions are elastic and of short duration

Question 7

What are some assumptions for Kinetic Theory?

Answer 7

• number of molecules is very large
• molecules are in constant and random motion

Question 8

What is meant by absolute zero?

Answer 8

Temperature where all substance possess minimum internal energy.