Thermodynamics 2

Question 1

State function or state variables.

Answer 1

State of a gas can be described by its pressure in a volume, temperature and composition variables like pressure, volume or temperature are called state variables or state functions. Because, their value depends only on the state of the system but not how it is reached.

Eg: - Pressure, volume, temperature, entropy, enthalpy, internal energy.

Question 2

Isothermal process

Answer 2

When a process is carried out in such a manner, where temperature remains constant.

Question 3

Isochoric process

Answer 3

It is a process during which the volume of a system is kept constant.

Question 4

Isobaric process

Answer 4

It is a process in which the pressure of a system is kept constant.

Question 5

Adiabatic process

Answer 5

It is a process in which there is no transfer of heat between the system and the surroundings. The walls which separate the system from the surrounding are called adiabatic walls.

Question 6

Describe the transfer of energy by heat.

Answer 6

• Transfer of energy in the form of heat the transfer takes place with the system and the surroundings or at different temperatures.
• (q) is Positive when the system absorbs heat.
• (q) is Negative when the system loses heat.

Question 7

Describe the transfer of energy by work.

Answer 7

• The transit of energy takes place in the form of work if the system and the surroundings are at different pressures.
• Consider a gaseous System which is enclosed in a cylinder having a movable piston. If the pressure of the system is high the piston will move upwards till the pressure of the system and the surrounding become the same that is work done by the system, so W is negative.
• If pressure of system is low the piston will be pressed down till the pressure of the system and the surroundings are equal that is work done on the system, so work done is negative.

Question 8

Internal energy.

Answer 8

It is the energy stored within the system. It’s a sum of different types of energy, electrical, mechanical etc…

∆U= Up - Ur
- Internal energy is also a state function.

Question 9

First law of thermodynamics.

Answer 9

The energy of an isolated system is constant. It is commonly stated as the law of conservation of energy that is energy can neither be created nor destroyed.

∆U= q + W
W= p∆V
∆U= q + p∆V
∆U = qv

change in volume remains same so ∆V=0 so p∆V = 0

=> ∆U =qv + p∆V

Question 10

mathematical expression of first law of thermodynamics

Answer 10

∆U= q + W