LAWS OF THERMODYNAMICS:

(i). Zeroth Law of thermodynamics:

If two bodies are in thermal equilibrium and a third body is in thermal equilibrium with any one of the first two bodies, then it can be inferred that all the three bodies are in thermal equilibrium. 

(ii). First Law of Thermodynamics:

        If any system is carried through a cycle then the summation of the work delivered to the surroundings is proportional to the summation of the heat taken from the surroundings.

            ¤∫         dW  α    ¤   ∫              dQ                    

¤∫         dW  = J    ¤   ∫              dQ     J is th proportionality constant known as the mechanical

                                    equivalent  of heat = 1 KJ / KNm

           

            ¤∫         dQ  -    ¤   ∫              dW / J  = 0

            ¤∫          [                                                                        [dQ  -    dW / J]  = 0

Path:

    If a system passes through a series of state point then it is said to describe a path.

Process:

    Whenever a state change occurs then the system is said to undergo a  process

Cycle:

    If a system starts from a particular thermodyanmic coordinate point, under goes different process and once again comes back to its initial state points it is said to undergo a cycle or thermodyanmic  cycle

Corollary:

(a)  Internal energy is a property.

    Consider a system of two cycles 1 A 2 B 1 and  1 A 2 C 1  

       Applying first law to cycle I: 1 A 2 B 1

1A∫2  [dQ-dW/J] + 2B∫1  [dQ-dW/J]  = 0

1A∫2  [dQ-dW/J] =  - 2B∫1  [dQ-dW/J] 

1A∫2  [dQ-dW/J] =  1B∫2  [dQ-dW] ---- (a)

Applying first law to cycle I: 1 A 2 C1

1A∫2  [dQ-dW/J] + 2C∫1  [dQ-dW/J]  = 0

1A∫2  [dQ-dW/J] =  - 2C∫1  [dQ-dW/J] 

1A∫2  [dQ-dW/J] =  1C∫2  [dQ-dW] ---- (b)

From (a) & (b) we get  1A∫2  [dQ-dW/J] =  1B∫2  [dQ-dW] =   1C∫2  [dQ-dW]

The quantity [dQ-dW/J] is independent of the path.

Any quantity, independent of the path is known as property.

     [dQ-dW/J] is a property.

But we have taken that [dQ-dW/J]= dU and  U is the internal energy for the given mass m. Therefore  internal energy is a property.

(b) Law of conservation of Energy.

    Energy can neither be created not destroyed if mass is conserved.

It is defined as the internal energy remains unchanged if the system is completely isolated.

    if Q=0 ;    W = 0 then  ∆U =0

(c)  Perpetual Motion Machine   of  I kind  ( PMM I) is impossible.

It is imposible to construct an engine which produces work without taking heat from the surrounding.
An engine which can produce work without taking heat from the surrounding is known as PMM I. This is not possible.