Text 8.7 Using the virial equation of state for hydrogen at 298 K given in problem 7 (text 8.6), calculate a. The fugacity of hydrogen at 500 atm and 298 K b. The pressure at which they fugacity is twice the pressure c. The change in Gibbs free energy caused by a compression of 1 mole of hydrogen from 1 to 500 atm. What is the magnitude of the contribution to (c) caused by the non ideality of hydrogen

Respuesta :

Answer:

a). P = 688 atm

b). P = 1083.04 atm

c).Δ G = 16.188 J/mol    

Explanation:

a). Fugacity 'f' can be calculated from the following equations :

[tex]$\ln \frac{f}{P}=\int^P_0\left(\frac{Z-1}{P}\right) dP$[/tex]

where, P = pressure ,  Z = compressibility

Now, the virial equation is :

[tex]$PV=R(1+6.4\times 10^{-4} P)$[/tex]  ........(1)

Also, PV=ZRT for real gases .......(2)

∴ [tex]$ZRT=RT(1+6.4\times 10^{-4} P)$[/tex]

  [tex]$Z=1+6.4\times 10^{-4} P$[/tex]

So from the fugacity equation ,

[tex]$\ln \frac{f}{P}=\int^P_0\left(\frac{1+6.4\times 10^{-4}P-1}{P}\right) dP$[/tex]

[tex]$\ln \frac{f}{P}=\int^P_0\left(\frac{6.4\times 10^{-4}P}{P}\right) dP$[/tex]

[tex]$\ln \frac{f}{P} = 6.4 \times 10^{-4} P$[/tex]

[tex]$f=Pe^{6.4 \times 10^{-4} P}$[/tex]

Putting the value of P = 500 atm in the above equation, we get,

f = 688 atm

b). Given f = 2P

    [tex]$2P=PE^{6.4 \times 10^{-4}P}$[/tex]

   [tex]$2=E^{6.4 \times 10^{-4}P}$[/tex]

  [tex]$\ln 2 = 6.4 \times 10^{-4}P$[/tex]

  ∴  P = 1083.04 atm

c). dG = Vdp -S dt  at constant temperature, dT = 0

Therefore, dG = V dp

[tex]$\int^{G_2}_{G_1}dG =\int^{P_2}_{P_1}V dp $[/tex]

            [tex]$=\int^{P_2}_{P_1}\frac{RT}{P}\left(1+6.4 \times 10^{-4}P\right) dP$[/tex]

           [tex]$=\int^{P_2}_{P_1}RT\frac{dp}{P}+\int^{P_2}_{P_1}RT6.4 \times 10^{-4} dP$[/tex]

[tex]$\Delta G=R[\ln\frac{P_2}{P_1}+6.4 \times 10^{-4}(P_2-P_1)]$[/tex]

[tex]$\Delta G=8.314\times 298[\ln\frac{500}{1}+6.4 \times 10^{-4}(500-1)]$[/tex]

Δ G = 16.188 J/mol