Lecture 3 Equilibrium thermodynamics

Question 1

What is equilibrium thermodynamics?

Answer 1

It is the systematic study of transformations of matter and energy in systems as they approach equilibrium.

Question 2

How many laws are there and what are they?

Answer 2

Four laws

Zeroth law - thermodynamic equilibrium is an equivalence relation. If two thermodynamic systems are in thermal equilibrium with a third, they are also in thermal equilibrium with each other.

First law - about the conservation of energy.

Second law - about entropy.

Third law - about absolute zero temperature. As a system asymptotically approaches absolute zero of temperature all processes virtually cease and the entropy of the system asymptotically approaches a minimum value.

Question 3

What are the three first law of thermodynamics laws i need to know?

Answer 3

The total energy of an isolated system always remains constant, although there may be a change from one form to another.

Any gain or loss of energy by the system must be exactly equivalent to the loss or gain, respectively, by the surroundings of the system.

Energy can neither be created nor destroyed, the only change which energy can undergo is a transformation from one form to another.

Question 4

What is the mechanical formulation of the first law?

Answer 4

dQ= dU +dW

Question 5

What are the limitations of the first law?

Answer 5

 While the first law establishes the equivalence between heat and work, it imposes no condition on their mutual convertibility. It never tells us under what circumstances and to what extent it is possible to convert one form of energy into another.

 First law tells us that the amount of heat lost by the hot body must be equial to that gained by the cold body but there is nothing in the first law which tells us that the heat has to flow spontaneously from the hotter to the colder body and not in the reverse direction.

 When we examine the relationship between heat and work, we notice that whereas different forms of energy can be readily and completely converted into heat, it is not possible to convert back heat completely into work.

Question 6

What is the phenomenological definition of entropy?

Answer 6

Self acting- the system performs work using its own energy. It doesn’t use an external source of energy. Heat cannot be transferred from the body with a lower temperature to a body with a higher temperature.

Question 7

Define second law of thermodynamics

Answer 7

The total entropy of a system must increase if a process is to occur spontaneously.

Question 8

The second law of thermodynamics for an isolated system:

Answer 8

1. Entropy does not change during reversible processes (dS=0) and increases during irreversible processes.
2. Only those processes can naturally take place where entropy will increase. All real processes are irreversible.
3. Entropy of closed and open systems may decrease (dS<0) if these systems give off heat to the environment (dQ<0).