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The coefficient of thermal expansion α = (1/V)(∂V/∂T)p. Using the equation of state, compute the value of α for an ideal gas. The coefficient of compressibility β is define by β = -(1/V)(∂V/∂p)T. Compute the value of β for an ideal gas. For an ideal gas, express the derivative (∂p/∂T)v in terms of α and β. Do the same derivative for van der Waals gas.

Answer :

Answer:

The coefficient of thermal expansion α is  

      [tex]\alpha  =  \frac{1}{T}[/tex]

The coefficient of compressibility

      [tex]\beta   =  \frac{1}{P}[/tex]

Now  considering [tex](\frac{ \delta P }{\delta T} )V[/tex]

From equation (1) we have that

       [tex]\frac{ \delta P}{\delta T} = \frac{n R }{V}[/tex]

From  ideal equation

         [tex]nR = \frac{PV}{T}[/tex]

So

     [tex]\frac{\delta P}{\delta T} = \frac{PV}{TV}[/tex]

=>  [tex]\frac{\delta P}{\delta T} = \frac{P}{T}[/tex]

=>   [tex]\frac{\delta P}{\delta T} = \frac{\alpha }{\beta}[/tex]

Explanation:

From the question we are told that

   The  coefficient of thermal expansion is [tex]\alpha = \frac{1}{V} * (\frac{\delta V}{ \delta P}) P[/tex]

    The coefficient of compressibility is [tex]\beta = - (\frac{1}{V} ) * (\frac{\delta V}{ \delta P} ) T[/tex]

Generally the ideal gas is  mathematically represented as

        [tex]PV = nRT[/tex]

=>      [tex]V = \frac{nRT}{P} --- (1)[/tex]

differentiating both side with respect to T at constant P

       [tex]\frac{\delta V}{\delta T } = \frac{ n R }{P}[/tex]

substituting the equation above into [tex]\alpha[/tex]

       [tex]\alpha = \frac{1}{V} * ( \frac{ n R }{P}) P[/tex]

        [tex]\alpha = \frac{nR}{PV}[/tex]

Recall from ideal gas equation  [tex]T = \frac{PV}{nR}[/tex]

So

          [tex]\alpha = \frac{1}{T}[/tex]

Now differentiate equation (1) above with respect to  P  at constant T

          [tex]\frac{\delta V}{ \delta P} = -\frac{nRT}{P^2}[/tex]

substituting the above  equation into equation of [tex]\beta[/tex]

        [tex]\beta = - (\frac{1}{V} ) * (-\frac{nRT}{P^2} ) T[/tex]

        [tex]\beta =\frac{ (\frac{n RT}{PV} )}{P}[/tex]

Recall from ideal gas equation that

       [tex]\frac{PV}{nRT} = 1[/tex]

So

       [tex]\beta = \frac{1}{P}[/tex]

Now  considering [tex](\frac{ \delta P }{\delta T} )V[/tex]

From equation (1) we have that

       [tex]\frac{ \delta P}{\delta T} = \frac{n R }{V}[/tex]

From  ideal equation

         [tex]nR = \frac{PV}{T}[/tex]

So

     [tex]\frac{\delta P}{\delta T} = \frac{PV}{TV}[/tex]

=>  [tex]\frac{\delta P}{\delta T} = \frac{P}{T}[/tex]

=>   [tex]\frac{\delta P}{\delta T} = \frac{\alpha }{\beta}[/tex]