Lansing, CHEM 151
Excerpt: ... ty The square root of the average of the squared velocities of the gas molecules in a sample. -Effusion and Diffusion: Effusion: The escape of a gas through a tine hole such as a pin hole in a balloon Diffusion: THe spreading out of a gas throughout an open space Graham's Law of Effusion: The rate of effusion of a gas is inversely proportional to the suqare root of its molar mass For two gases under identical conditions, SEE PAPER NOTES - Deviations from Ideality From PV = nRT (ideal gas equation) n = PV / RT for 1mol of an ideal gas, PV/RT = 1 at all pressures -The higher the temperature, the smaller the deviation from ideal behaviour Van der Waals Equation : Real gases have definite volumes and attract eachother. Refer to the postulates of the Kinetic Molecular Theory. The Van der Waals equation contains terms that make corrections for teh volume of molecules and attraction between molecules. Real Gas Equation: P = (nRT / V-nb) - n^2a / V^2 nb = correction for volume of molecules n^2a / V^2 = Correct ...
Ohio State, CHEM 122
Excerpt: ... Molecular Effusion and Diffusion The lower the molar mass, M, the higher the rms. Kinetic Molecular Theory Graham's Law of Effusion Effusion is the escape of a gas through a tiny hole (a balloon will deflate over time due to effusion). 3RT r1 u1 M2 M1 = = = 3RT r2 u2 M1 M 2 12 Diffusion and Mean Free Path bromine diffusion Real Gases: Deviations from Ideal Behavior PV =n RT 13 Real Gases: Deviations from Ideal Behavior As the gas molecules get closer together, the smaller the intermolecular distance. Real Gases: Deviations from Ideal Behavior The higher the temperature, the more ideal the gas. Because they move farther apart ! (So, the volume has to expand for this to be true) 14 Real Gases: Deviations from Ideal Behavior The van der Waals Equation P= nRT n2a - 2 V - nb V Corrects for molecular volume Corrects for molecular attraction General form of the van der Waals equation : 2 P + n a (V - nb ) = nRT V2 End of Chapte ...
Virginia Tech, CHEM 3615
Excerpt: ... Lecture 5 September 9, 2008 Virial Expansions Empirical Treatment of Real Gasses Consider the Compression Factor, Z Z= For the case of a perfect gas, Z = 1 For the case where finite size effects matter, pV is larger than expected for an ideal gas so Z > 1 For the case where attractive interactions are important, pV is smaller than expected for an ideal gas so Z < 1 Quantifying these Effects, the van der Waals Equation of State (1) Molecular Volume correction to the perfect gas law: pV RT p= (2) RT where b = molar volume = m3/mol (accounts for repulsions) Vb Attractive Interactions p = pideal a V2 , where a = attractive interactions which reduce pressure units = pressure x volume2 (3) Putting the two together yields the van der Waals Equation of State p= or a p + (V b ) = RT V2 RT a valid for V > b V b V2 p= RT b V 1 V a V2 Page 1 of 8 The van der Waals equation of state is valid for gases at low pressure where the pVT ...
Georgia Tech, CHBE 2110
Excerpt: ... ChBE 2110 Practice Questions for Final Exam Fall 2007 Professor Gallivan From Elliott and Lira: o 7.2, Derive in terms of Z(,T) o 7.6 o 7.25, Instead of Peng-Robinson, use (1) methane chart, (2) ideal gas law (cp/R = 4.298, and (3) the van der Waals equation . o Suppose you are given a cubic equation of state of the form P = f(V,T) and coefficients for the Antoine equation. Explain how you would construct a phase diagram based on this information. Be sure to make a sketch. Explain how you will find the critical point. Attempt to work these in 2 hours. You may use any tables in the text, but try not to refer to the remainder of the text since the exam will be closed book. Since you can bring 3 single sided pagse of notes to the exam, you may wish to make these sheets first and use them to take the practice exam. (And presumably then revise it after taking the practice exam.) We will discuss these questions in the office hour review session on Friday at 5 pm. ...
UWO, CHEM 024b
Excerpt: ... States of Matter: I Real Gases By the end of this lecture you will be able to: (1) Differentiate between real and ideal gases. (2) Understand how the ideal gas law can be modified to account for the differences. (3) State and manipulate the van der Waals equation . (4) Know what intermolecular forces and dipole moments are. (5) Correlate the dipole moment of a molecule to its intramolecular bonding. (6) Know what polar covalent bonds are and their relationship to electronegativity. (7) Understand attractive forces between non-polar molecules. (8) Understand how the size, polarity and symmetry of molecules correlate with the van der Waals equation . (1) What is a real gas? All gases are real gases. The ideal gas is simply a concept and does not actually exist. Real gases behave like the ideal gas at low pressure and high temperature. In real gases: (a) Molecules have significant volume. (b) There are significant forces between molecules. The ideal gas equation can be modified to account for thes ...