Real Gases.doc

REAL GASES

Submitted By: Cesar Ian A. Caermare Izel Marion Nicole C. Hernando

Date Submitted: July 21, 2012

Submitted to: Prof. Sheeva Yahcob-Saddalani Chem 142 Lab Instructor

ABSTRACT The study was carried out to graphically evaluate the behavior of real gases at changing conditions and the ability of selected real gas equations of state to predict P-V-T relationships of gases. The pressure exerted by carbon dioxide at 31.1 °C and 100 °C was plotted against molar volume and ideal, van der Waals, and experimental isotherm were evaluated. With these, the absolute accuracy of van der Waals equation isotherm was evaluated by comparing its plot against ideal isotherm. Redlich Kwong equation of state was validated by attempting to predict the P-V-T relationship of CO2. Van der Waals equation of state is best applicable to carbon dioxide at 31.1 °C as the accuracy of the van der Waals isotherm is in unity with the ideal isotherm at a wide range at this condition. Redlich-Kwong isotherm also best describes CO2 at 100 °C since the graph shows that the deviation of this isotherm is very less to ideal isotherm. In part two, Redlich-Kwong and Dieterici equations of state were evaluated using the thermodynamics quantities of selected samples of gases and then plotted to better understand the equations being evaluated. The two equations best describe water vapor and ammonia gases as manifested by the plot produced by these equations. However, the slopes produced by Redlich-Kwong EOS approximate the gas constant, R value compared to Dieterici EOS. Thus, Redlich-Kwong EOS has better applicability to water vapor and ammonia. Other equations of state are recommended for validation using the other gas samples INTRODUCTION: Gas is a state of matter that is known to have particles which are very far apart from each other and that they are in constant random motion. A gas can behave as perfect or real gas. A Perfect Gas is proposed by the Kinetic Molecular Theory as a very minute particle size negligible compared to the distance travelled by the molecule and which aside from being very far apart and in random motion, there is no transfer of energy during collisions. Real Gas system on the other hand differs from a Perfect Gas system because there is transfer of energy in the collision of gas molecules, resulting to molecular interactions. However, real gases approximate perfect gas behavior at very low pressure and significantly high temperature. A real gas deviates increasingly from ideality as it is compressed and cooled to near the point at which it will condense into liquid. The deviation from the ideal gas is particularly important at high pressure and low temperature. The properties of the real gas can be express in terms of isotherm and compression factor (Z). Because perfect gas has compressibility factor equal to 1 under all conditions, deviation of Z from 1 is a measure of imperfection. At very low pressure all gases are expected to have Z≈1 and are behaving nearly perfectly. At high pressure all gases have Z>1, signifying that they are more difficult to compress than the perfect gas. At intermediate pressure most of the gases have Z