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Phase Equilibrium

Determine diffusion coefficient, Solubility, Henrys ConstantThe enthalpy of solution of carbon dioxide in Stoddard solvent in the range of 18 - 35

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Phase Equilibrium

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    1. Phase Equilibrium

    2. Determine diffusion coefficient, Solubility, Henrys Constant The enthalpy of solution of carbon dioxide in Stoddard solvent in the range of 18 - 35°C and at 1.0 atmosphere pressure.

    3. Introduction Diffusion Coefficient Measures the rate of diffusion Time-dependent Solubility Measures maximum amount of gas dissolved in liquid Time-independent Henry’s Law constant Dissolved gas in liquid is proportional to partial pressure in vapor phase Heat of mixing Correlation between Henry’s Law constant and T

    4. Determination of diffusion coefficient from experimental data

    6. Thus the unsteady-state differential equation representing concentration changes with time and position is: Solution of Fick’s 2nd Law using the boundary conditions described is: Solve for the number of moles added up to a time t: If one plots NT versus t1/2, the slope of this line is equal to 2ACi (D12/?)1/2

    7. Solubility Henry’s Law constant The solubility of a gas in a liquid solvent may be represented to good accuracy at dilute concentrations of the dissolved gas by Henry's Law: f = H X where f is the fugacity of the gas in the gas phase in equilibrium with the liquid phase of concentration X of dissolved gas. H is the Henry’s law constant, which is a function of temperature. Thus, by measuring the solubility one can obtain an estimate of the Henry's law constant.

    8. n = gram moles of carbon dioxide absorbed in the liquid phase PT = corrected barometer reading = vapor pressure of Stoddard Solvent at cell temperature Tp = temperature at the pump Tc = temperature of the cell (bath temperature) = total gas volume delivered from the pump to the cell Vcg = volume of the gas phase in the cell Zp = compressibility factor of CO2 at pump T and PT Zc = compressibility factor of CO2 at cell T and PT Vd = dead volume in the system (cc)

    9. The fugacity, f, can be determined from the Lewis and Randall Rule, which gives f = fugacity of CO2 in the gas phase fo = fugacity of pure gaseous CO2 at PT and cell T y = mole fraction of CO2 in gas phase Thus by definition: the fugacity coefficient for pure CO2 in the gas phase at cell T and P T

    10. Use Henry’s Law coefficients at the three experimental temperatures to obtain the heat of mixing: Plotting ln(H) vs. 1/T gives a line with a slope of ?Hmix/R. ?Hmix is expected to be negative, which would indicate that CO2 and Stoddard solvent are more energetically stable than apart (i.e., the interactions are favorable). Heat of Mixing

    15. Penetration Model

    16. References Koretsky, Milo D. Engineering and Chemical Thermodynamics. John Wiley & Sons, Inc., 2004. Ophardt, Charles E. Virtual Chembook. Elmhurst College, 2003. [Online] Available at: http://www.elmhurst.edu/~chm/vchembook/174temppres.html http://en.wikipedia.org/wiki/Lake_Nyos

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