Thermodynamics defination

Thermodynamics equilibrium -:

A system said to be exist in a state of thermo - dynamics equilibrium, when no change in microscopic properties .

Microscopic properties-:

1. Mechanical -: Equality of force.

2. Physical -: Equilibrium of temperature. 

3. Chemical -: Equilibrium of chemical com - position .

 Pure substance -: A substance is said to be     pure substance, if it is homogeneous chemical composition and homogeneous is chemical .

 Steam         H2 + o2        H2 + o

-----------        -----------        -----------

Water             H2o            water

( pure)        ( not pure )   ( not pure)

Adiabatic process -: A process is said to be adiabatic if there is no heat transfer from the system or to the system. 

Generalise equation for adiabatic process--

 PV^r = c ( r = adiabatic index)

 W = P1.V1 - P2.V2 / r - 1

Polytropic  process-: In adiabatic process there is no hear transfer only work transfer,

But in polytropic process there is heat trans-fer as well as worktransfer. 

Generalise equation for polytropic process--

   PV ^ n = c   ( n = polytropic index ) 

    r = Cp / Cv
   Cp - Cv = R                                                               W ( polytropic ) = P1.V1 - P2.V2/ n-1
   (r > 1 ,   n > 1 ,   r > n ).

Wet region-: It is the region where vapour and liquid exest in equilibrium. 

In this case- T ( actual) = T ( saturated)

Dry ice -: Dry ice , that is called solid co2 , when exposed to 1 atmospheric pressure , it 

Vaporized directly without absorbing latent heat of sublimation.                                                                             The slop of sublimation and vaporization is positive. Also slop of fusion is positive or all the case except water.

Triple point  -:  The triple point is a point   where all three phases co- exist. the triple   point of water is 4.58 mm(p) of Hg and tem-

 Perature is 0.01 ° C or 237.16 K.

Perceptual motion machine -1 and Heat transfer

Perceptual motion machine-1 -: perceptual motion machine, which devo-loped works continuously without absorbing some other form of energy, if sach a machine is develop -  ed it would first law of thermo-dynamics. 

 Q = 0 --- PMM -1 --- w

PMM -1 is impossible. 

dv = m.Cv.dT ,      

dH = m.Cp.dT

Here  U = f ( t )

Heat transfer -: 

Heat transfer in various non - flow process--

1. Constant volume process -:

Heat transfer in a constant volume process for a closed system is equal to change in thermal energy .

dQ = du + P. dv

When , v = Constant,  dv = 0 dw = 0

Then dQ = dv

2.  Constant pressure process-: 

Heat transfer for a constant pressure process is equal to change in Enthalpy. 

dQ = du + P. dv

When , P = Constant 

dQ = du + P ( dv )   , dQ = d ( u + Pv )

dQ = dH

3. Isothermal process-: 

When an ideal gas undergoes isothermal process , heat transfer is equal to work .

dQ = du + P.dv

When , T = Constant  if  u = f ( t ) du = 0

dQ = dw .

Thermodynamics MCQ - 05

Q.1 At very high pressure , an ideal gas as compared to a real gas occupies ______.

A. Same volume 

B. More volume 

C. Less volume 

D. None of these 

Ans-: B

Q.2 Superheated vapour behaves like ___.

A. As steam 

B. Exactly as gas 

C. Water

D. Approximately as a gas

Ans-: D

Q.3 Which law states that , the specific heat of a gas remain constant at all temperature and pressure?

A. Regnault's law

B. Boyle's law 

C. Joules law 

D. Avogadro's law

Ans-: A

Q.4 Thermocouple based on the ____.

A. Temperature of two bodies

B. Atmospheric pressure 

C. See - back effect 

D. Atmospheric temperature 

Ans-: C

Q.5 Air contains following parts of the oxygen. ( on the weight basis )

A. 24 

B. 23

C. 30

D. 73

Ans-: B

Q.6 In thermodynamics cordinates properties of substance like , pressure, temperature and density are ______.

A. Real function 

B. Point function

C. Cyclic function 

D. Thermodynamics function 

Ans-: B

Q.7 which of the following is not a path function?

A. Heat

B. Work 

C. Kinatic energy 

D. Thermal conductivity 

Ans-: D

Q.8 In a cycle heat us rejected at____.

A. Constant pressure 

B. Constant temperature 

C. Constant volume

D. All of the above 

Ans-: A

Q.9  Flow of steam through a nozzle is ___.

A. Constant flow

B. Adiabatic flow

C. Isothermal flow

D. Constant pressure flow

Ans-: B

Q.10 The ratio of number of moles of a gas to total number of moles is known as _____.

A. Ideal gas 

B. Mole fraction 

C. Enthalpy 

D. Molecular ratio

Ans-: B

Q.11 Real gas follows,  PV = nRT ?

A. Yes 

B. No

C. At constant temperature 

D. At constant pressure 

Ans-: No 

Q.12 The region where vapour and liquid exest in equilibrium is called ___.

A. Hot region 

B. Wet region

C. Cold region

D. None of these 

Ans-: B

Q.13 Solid "Co2" is also known as _____.

A. Dry solid 

B. Dry ice 

C. Dry Co2

D. Dry gas 

Ans-: B

Q.14 The triple point is a point , where ___.

A. Two phases co - exist 

B. Three phases co - exist 

C. No phase co - exist 

D. None of these 

Ans -: B

Q.15 Triple point of water is ____.

A. 4.58 mm(p) of Hg

B. 0

C. 45.8 mm (p) of Hg

D. 1 

Ans -: A

Physical meaning of entropy and Enthalpy

Entropy is a measure of molecular dis - oderness or randomness, greater is the disorderness lesser the efficiency.                    " Entropy change of univers "

  ds >or = dQ/ T

  ds (universe) > or = 0 

( universe is a isolated system)

ds ( system) + ds ( surrounding) > or = 0

Entropy of the system can increase or decrease or it can remain constant. Similarly the entropy of surrounding can increase or decrease or it can remain constant but " the overall change in Entropy of univers can never decrease.

Q. What is source and sink?

Ans-: source-: source is a reservoir, which supplies thermal energy without undergoing any temperature change .

Sink -: It is a reservoir which absorb thermal energy without undergoing any temperature change. 

Enthalpy -: In thermodynamics the term " u + Pv " is taken as Enthalpy. 

H = u + Pv

It is an extensive property and generally express in " KJ".

Specific Enthalpy  H/m = h = KJ/Kg

Zeroth law and thermometer

Zeroth law of thermodynamics -:

Zeroth law of thermodynamics is that , when a body "A" is in thermal equilibrium with body "B" and the body "B" is in thermal equilibrium with body "C" , then automatically body "A" will be in thermal equilibrium with body " C".

       The concept of the thermometer  is based on the " zeroth law of thermodynamics "

Thermometer -: Thermometer is a device or a measuring instrument which is used to measure temperature ( how hot or cold some- thing is ).

Types of thermometer--

1. Resistance thermometer 

2. Thermo couple -: It is based on the see - back effect .

3. Constant volume gas thermometer-:

    It is works on the pressure change .

4. Constant pressure gas thermometer-:

    It is works on the change in volume. 

Throttling process

Throttling process -: when steam is pass from a respectable path such as partially opened valve , it's pressure reduces but the entropy of the steam remian constant this prcess is known as throttling process.

                In this process there is no change in Enthalpy from state one to state two , h1 = h2

,no work is done and process is adiabatic ,

 Q= 0.

Concept of entropy

First law of thermodynamics says that energy is constant, it does not give any direction for a particular process. 

           But the second law of thermodynamics gives direction of processe  the concept of entropy hence second law of thermdynamics also known as "directional law " .