Constant temperature process | Isothermal process

-
A constant temperature process is also called isothermal process is one type of thermodynamic process during the temperature is constant. The term isothermal is derived from the Greek word 'ISO' means constant or equal and "THERM' means temperature. 

What is the constant temperature isothermal process?


The process in which the temperature of the working substance remains constant during its expansion or compression is called isothermal or constant-temperature process. This will happens under isothermal conditions such as melting or evaporation these two are phase changes isothermal processes. The working substance remains in perfect thermal contact with the surroundings so that the heat sucked in or squeezed out is compensated exactly for the mechanical work done by or on the gas respectively. So, it is obvious that in an isothermal process two things happen which are noted below. 
  • There is no change in temperature
  • There is no change in internal energy. 

Example of the isothermal process: 

  • Condensation process. 
  • All the reactions going on in the refrigerator as the constant temperature maintained in it. 
  • The melting of ice at zero degrees Celcius. 
  • The reaction in a heat pump. 

Theoretical explanation: 


Isothermal constant temperature process
Constant temperature isothermal process

The isothermal process is represented in the P-V diagram in the above figure. 

Now, we know that, 

Q1-2 = dU + W1-2

 Hence, during the isothermal expansion process of the gas, 

 Heat added = Work done by the gas

 Similarly, the isothermal compression process of the gas, 

 Heat subtracted = Work done on the gas 

 Now, consider m kg of a perfect gas is expanded isothermally, which is shown in the figure.

 Let V1 = Initial volume of gas
P1 = Initial pressure of a gas 
V2 = Final volume of gas
P2 = Final pressure of a gas 
The work done during the isothermal expansion process is given by, 

W1-2 = Area under the curve 1-2

W1-2 = P1 V1 Loge (V2 / V1) = 2.3 P1 V1  Log (V2 / V1)

W1-2 = 2.3 m R T Log (V2 / V1) = 2.3 m R T Log (P1 / P2) 

In general, W = 2.3 P1 V1 Log r = 2.3 m R T Log r 

 Where r is expansion ratio when gas is heated or compression ratio when gas is cooled. 

 Now, you also learn what is the formula of expansion ratio?

 Expansion ratio (r) = Volume at the end of expansion / Volume at beginning of an expansion

 Compression ratio (r) = Volume at the beginning of compression / Volume at end of a compression

Comments

Post a Comment

Popular posts from this blog

Difference between characteristic and universal gas constant

-
Some important point on the difference between characteristics gas constant and universal gas constant are explained below. Let us check out one by one below. You can also check out characteristics equation of gas , and general gas equation to know more about it. Difference between characteristics gas constant and universal gas constant: Constant gas characteristics vary from gas to gas but the constant of universal gas is fixed. If you working at human scales, then use universal gas constant, whereas if you want to gas constant that defined per unit mass of a specific gas, then use the specific gas constant.  The characteristic gas constant in equation P = RT is the value of R for a given gas for use. It is equal to the constant of universal gas divided by the molar mass of the particular gas. Characteristics gas Constant applicable for an ideal gas, whereas universal gas constant applicable for a real gas.  Units: Characteristics gas constant - k J / kg K and Univers
Read more

Varignon's principle of moments | Varignon's Theorem

-
Image
Varignon's theorem also called the principle of moments.  Varignon's Principle: Varignon's principle states that if a number of concurrent forces acting on a particle are in equilibrium, then the algebraic sum the moments that each force creates about a single point will be equal to the moment of their resultant force about the same point.   Varignon's Theorem From the above figure, F1 and F2 are two concurrent forces and their resultant is R. The moment produced by R with respect to a moment center O is R × d. The moment produced by the force F1 and F2 is respectively F1 × d1 and F2 × d2.  As per varignon's therorem R d = F1 d1 + F2 d2 Notes: This theorem initially stated for two concurrent forces, but, it is true for any system of forces and any number of concurrent or coplanar forces.  One of the practical applications of this theorem is to find the unknown reactions when a system is known to be in equilibrium under the acti
Read more

Difference between moment and couple

-
Moment and couple are two important concepts found in mechanics. They both terms describe the effect and cause of rotation in the system of forces , particle systems, and rigid bodies too.  What is a moment of a force? The turning effect produced by a force applied to a rotational system or on the body at a distance from the axis of rotation is called the moment of force . The moment of a force is the product of the force and the perpendicular distance of the point, about which the moment is required and the line of action of the force. What is a couple OR moment of a couple?   In mechanics, a couple refers to two equal and opposite forces, whose line of action is different from a couple . The couple also called a force couple or pure moment.  Points of difference between moment and couple are discussed below. So let us check out some key differences between them to know more about it.  Difference between moment and couple: The moment is the
Read more