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Thermodynamics system ?it’s easy if you do it smart.


Thermodynamics system:- A thermodynamics system is a group of material and radioactive constant .

Its property may be describe by thermodynamic state variable state as Temperature , boundary , Introphy , internal energy and pressure.

Important Topic We Discuss

  1. Type of thermodynamics system
  2. Define
  3. Thermodynamics property
  4. Energy
  5. Zeroth law the thermodynamics
  6. First Law of thermodynamics
  7. Second law of thermodynamics
  8. Important Questions

Type of thermodynamics system

  • Open system
  • Close system
  • Isolated system
  • Homogenous system
  • Hetrogenous
  • Adiabatic system
  1. Open system :- In this system heat and mass transfer is called open system
  2. Close system :- These transfer of only many be energy and no transfer of mass is called close system.
  3. Isolated system :- There is no transfer of mass and energy to from the system is called isolated system.

Define :-

Thermodynamics :- Thermodynamics deals with the heat convert to power (work) and power to heat. This is a thermodynamics.

  • Energy :– Capacity of doing work is called energy.
  • Power :- Rate of doing work is called power.
  • Boundary :- Separate system from surrounding , boundary may be real or Imaginary.
  • Surrounding :– Anything external to system.
  • Universe :– A system and its surrounding together form a universe.

Thermodynamics property

Charactertics of system which can be measure types of property

  1. Intensive  property
  2. Extensive property
  • Intensive property :- Property does not depend on mass

Eg.- pressure , temperature , density etc.

  • Extensive property :- Property which depend on mass or size of system.

Eg.-mass , volume , energy , enthalpy , entrophy .

Hetrogenous system :– This is a system which consist two or more homogenous phase. There is sudden change in properties at the phase (state) is called hetrogenous system.

Eg. –Oil and water , mixture of benzene and water etc.

Homogenous system :- The system consist only one phase is called homogenous system.

Heat :- Heat is define as the energy transfer of mass over the boundary of a system slack to the difference in temperature . Its SI unit is joule (J).

Work :- Work is to be complete by a system it the role of effect of the system boundaries can be reduces to the raised of a weight.

Difference between Heat and Work

Heat can be converted absoluted into work exam in the most perfect engine.Work can be converted  absoluted into heat
It is low grade energy.It is high grade energy.
In heat transfer temperature difference is required.No temperature is required for work.
In a stable system there is not restseacticy far transfer of heatIn stable system there is not work transfer.
Heat supplied to system is taken as positive and heat rejected by system as negative.The work done on system as negative and by the system as positive.


     Type of energy

  1. Kinetic energy
  2. Potential energy
  1. Kinetic energy :- Kinetic energy is energy possess by an object in motion.
  2. Potential energy :- Potential energy is the energy hold by an object for of its position relative to other objects , stresses within itself , its electric charge , or other factors.

Do you know more about Kinetic energy , Potential energy click at the link.

Equilibrium :- A state of thermodynamics equilibrium is to the exist in a system there is no change in any microscopic property is register.The system is assume to be isolate term of its surrounding known as equilibrium.

Thermodynamics process :-When a system change its state from an equilibrium state to another equilibrium state.

The path of successive state through which system process is define as thermodynamics process.

Reversible process :- A process which can be reverse direction and the system retracts the same path and the same equilibrium state is define as reversible process.

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Irreversible process :- A process said to be irreversible if a system , passed through a sequence of non-equilibrium state. An irreversible process can not come back to the original state.

Quasic static process :- When the process carry out in such a manner that can every instead the system deviation from the thermodynamic equilibrium is very small than the process is known as Quasic-static process.

Pressure :

It may be define as the normal forced a exerted by a system against unit area of the surface.                                             Pressure   =    Force/area

Where F is the normal force and A is the area . SI unit = n/m2

Atmospheric pressure :- It is the pressure exert by the air on the surface of the earth.

Absolute pressure :- It is define as the pressure acting on a surface pace the interacting of the fluid particles.

Temperature :- Temperature is an intensive property which determine the degree of hotness.

The level of heat of intensity of the body temperature of body is measure with the help an instrument known as “Thermometer” which look like a glass tube.

Specific weight :- It is define as weight per unit volume. It is denote as ‘w’ specific weight.

                   Specific weight =w/v

          SI unit of specific weight = N/m3

Mass density :– It is define as mass per unit volume. It is denote as ‘P’ mass density.

                             Mass density (P) = M/V

                   SI unit of mass density = kg/m3

Specific volume :- It is the reciprocal of mass density the specific volume of a system is the volume occupy by the unit mass of system is define as specific volume.

                   Specific volume =  volume/mass

          SI unit of specific heat = m3/kg

Zeroth law the thermodynamics

Its two body A or C are equilibrium and it A is the equilibrium  to the third body B the body C is also equilibrium to B.

“It make all body balance with respectively”.

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First Law of thermodynamics

If some heat is supply to a system which is capable of doing work.

Then the quantity of heat absorb by the system will be equal to the sum of increasing in it internal energy and the external work done by  the system on the surrounding.


∆Q = heat supplied to system by the surroundings

∆W = work done by the system on the surroundings

∆U = change in internal energy of the system

 Them according to the first law of thermodynamics

       ∆Q = ∆U + ∆W

Suppose the system is a gas contain  in a cylinder provided with a movable piston. Then the gas does work in moving the piston. The work done by the system against a constant pressure P is

∆W = force * distance

 = presuure *area *distance


Or ∆W = P∆V

Where ∆V = Adx = the change in the volume of the gas.

       So the first law of thermodynamics takes the form,

              ∆Q = ∆U  +  P∆V

Second law of thermodynamics

There are many process in which energy is conserve and yet they are never observe.

The principle which disallow such phenomia ( as discussed in limitation of first law of thermodynamics ).

It consistent with the first law of thermodynamics is called second law of thermodynamics.

Kelvin – plank statement :- It is impossible to construct an engine , which will produce no effect other than extracting heat from a reservoir and performing an equivalent amount of work.

Clausius statement :- It is impossible for a self acting machine , unaided by any external agency , to transfer heat from a body to another at higher temperature.

 State the Limitation of second thermodynamics

  1. The second law of thermodynamics can not be prove directly. But its validity has not be contradict by any machine design as far.
  2. It is applicable to a cyclic process in which the system returns to its original state after a complete cycle of changes.
  3. It makes no predictions as to what will happen under certain conditions but simply states what will happen under given set of condition.


Q1. Define thermal equilibrium.?

Ans. Thermal equilibrium :- Two system are said to be in thermal equilibrium with each other if they have the same temperature.

Q2. State the sign conventions used in the measurement of heat , work and internal energy.

Ans. Sign convention used :-
1. Heat absorbed by a system is positive. Heat given out by a system is negative.
2. Work done by a system is positive. Work done on a system is negative.
3. The increase in internal energy of a system is positive. The decrease in internal energy of a system is negative.

Q3. What is thermodynamics process? Mention its different types .

Ans. Thermodynamics  process :- A thermodyamics process is said to occur if the thermodyamics variable of a system undergo a change with time.

Different type of thermodynamics processes are as follows :-

1) Isothermal process :- It is a thermodynamic process which occurs at a constant temperature.

2) Isobaric process :- It is a thermodynamics process which occurs at a constant pressure.

3) Isochronic process :- It is a thermodynamic process which occurs at a constant volume.

4) Adiabatic process :- It is a thermodynamic process in which there is no exchange of heat energy between system and surrounding.

Q4. Define heat engine. Explain its working principle.

Ans. Heat engine :- It is adevice which converts continuously heat energy into mechnical energy in cylic process.



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