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Mechanical Properties Of Fluids

Question
CBSEENPH11019630

What is the equation of state for isothermal process? Plot P versus V graph and P versus T graph for isothermal process for an ideal gas. Discuss the isothermal process using first law of thermodynamics. 

Solution
An ideal gas equation is given by, 
                   PV = nRT 
In an isothermal process, temperature T is constant.
Therefore the equation of state for isothermal process reduces to, 
                    PV = constant 
The graph of P versus V  and P versus T for an isothermal process is as shown below. 
 
Now, according to first law of thermodynamics, 
increment straight Q space equals space increment straight U space plus space straight P increment straight V space

For space an space isothermal space process comma space

space space space space increment straight U space equals space straight C subscript straight v increment straight T space equals space 0 space left square bracket Temperature space remains space constant right square bracket space

therefore space increment straight Q space equals space straight P increment straight V space equals space increment straight W space

In space an space isothermal space expansion comma space

space space space space space space increment straight V space greater than thin space 0 space

rightwards double arrow space increment straight Q space equals space straight P space increment straight V space greater than space 0 space

That space is comma space in space an space isothermal space expansion comma space
work space is space done space by space the space gas space and space heat space is space absorbed
space by space the space gas space equal space to space work space done space by space the space gas. space

In space isothermal space compression comma space

increment straight V space less than space 0 space

rightwards double arrow space increment straight Q space equals space straight P increment straight V space less than 0 space

That space is comma space in space isothermal space compression comma space work space is space done
on space the space gas space and space heat space is space released space by space gas space equal
to space work space done space on space the space gas. space