- Evaluate the compressibility factor of two different gases CH4, and C3H8 as a function of pressure and temperature. - Compare values of z-factors determined in this experiment with published values from zfactor charts. Definition of the z-factor The compressibility factor, z, is the ratio of the volume actually occupied by a given mass of gas (n) at given pressure and temperature to the volume that the same mass of gas would occupy if it behaved like an ideal gas at the same pressure and temperature. Thus: Z=Vreal/Videal The compressibility factor equation of state for a real gas is: pV=znRT where, p=absolutepressureV=volumeofgasn=numberofmolesR=universalgasconstantT=absolutetemperature For an ideal gas, by definition z=1. Therefore for the same amount of gas (n) we can calculate its ideal gas volume as, VMd=nRT/P Procedure You must repeat the following steps for each gas and for 3 different temperatures. So if you decide to take about 15 pressure points per temperature per gas, you will have 90 data points. Part A. 1. Set temperatures. Use Tr values 1.2, 1.6 and 2.0 to determine the temperature. Tr=T/Tc 2. Fill the gas with low pressure. 1.1 bar is close to atmospheric pressure. 3. Note the moles charged in the PVT cell and record this value. 4. Increase the pressure on the PVT cell by adding weights. Record the molar volume (V). 5. Design the pressure steps so that you have enough number of points to determine z up to the highest allowable number of weights in the cell. Pick your number of points with logic. 2 is too little, and 100 is too many. Justify why you selected the number of points you selected. 6. For each data points, note the cell volume, molar volume, moles, the pressure and the temperature. 7. Calculate ideal gas volume for every data point collected. 8. Determine the z-factors for each point. 9. Calculated the reduced pressure. Pt=P/Pt Part B. 1. Charge the PVT cell with same gas as in part A, same temperature but begin with the max pressure you ended in the previous experiment. 2. Start with about 30cm3 of volume. 3. Lock the volume using V. 4. Increase the pressure in the cell by charging the cell with more mass (i.e. moles) of the component. 5. Record the number of moles, pressure, and temperature each time. The volume will be fixed. 6. Calculate the reduced pressure Pr. 7. Add these new values to the graph you have. Follow Lab Format and explain - Gas Compressibility - Explain all unit conversion and equation used in this lab - Add Z-factor graph for C1 and C2 using the Tr values of 1.2,1.6, and 2.0