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Dear Expert
Gas : 2CO(g) + O2(g) <---> 2CO2(g)
" The effect of an addition of an inert gas depends on the conditions at which it is added.
If the inert gas is added at constant volume, the total pressure increases, but the partial pressure of each component gas is unchanged, thus the equilibrium position does not shift.
If the inert gas is added at constant pressure, the volume will increase(dilution effect) and the equilibrium position will shift in the direction that increases the total number of moles of gas"
Qn 1: What does it mean by "Added at constant volume" and "added at constant pressure"? Is it adding the gas without increasing the volume of gas or pressure? How is it possible to maintain the volume while changing the pressure since they are so related to one another? If the number of moles of gas in the container increases in volume, wouldn't the pressure exerted on the container increase?
Regards,
Washy
Hello Mr. Washington!
Ah, PV=nRT. Learn it, love it, live it. Whenever you do ideal gas problems, write out what is known, what is constant, and what is increasing or decreasing from state 1 to state 2. (In the top example, V1=V2, R=R, n1<n2 etc) This may help you keep track of all your parameters.
When we say constant volume, the container is reinforced (such as a steel cylinder) so that the gas cannot expand or contract, forcing the volume to remain constant. In your example, the total pressure would increase because the number of moles of gas would increase.
Total pressure at constant volume = Pressure from Gas A + Pressure from Added Gas B
However, the amount of pressure exerted on the sides of the container *only from gas A* does not change. A's *partial pressure* does not change. However, we're stuffing more moles of gas in the cylinder by adding B (n1<n2), adding B's partial pressure to the sum. You're right, the walls of the container see an increase in pressure, because we're adding gas in total, even though the partial pressures from each component do not change.
In the above reaction, if we add equal (molar) amounts of CO and CO2, the equilibrium of the reaction will not change; we are adding balanced amounts. We know this from the molar ratio of the equation as well as Le Chatelier's Principle. If we were adding an excess of one reactant (say, O2) the equilibrium may shift to make more 2CO2, because then we'd have fewer, larger molecules banging around in the container, and under constant volume that equilibria would have less energy/entropy requirements to maintain.
If we keep the pressure constant but permit an expandable container (e.g. a balloon), the volume can change. Equilibrium shifts to be the lowest energy it can be, which often means an increase in entropy. The highest entropy in this situation would be the equilibrium position that had the highest number of moles of molecules flying around in the largest volume possible, along with a possible loss of heat.
Does this help?
Stuff to read up on:
http://en.wikipedia.org/wiki/Le_Chatelier's_principle
http://bouman.chem.georgetown.edu/S02/lect8/lect8.htm (Le Chatelier and the Ideal Gas Laws)
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Trista Robichaud, PhD
Expertise
No homework questions, especially ones copied and pasted from textbooks. I will answer questions about principles or give hints, but I do not do other's homework. I'm comfortable answering basic biochemistry, chemistry, and biology questions up to and including an undergraduate level of understanding. This includes molecular biology, protein purification, and genetics. My training/inclination is primarily in structural biology, or how the shapes of things affect their function. Other interests include protein design, protein engineering, enzyme kinetics, and metabolic diseases such as cancer, atherosclerosis, and diabetes. My chemistry weaknesses are that I do not know organic or inorganic synthesis well, nor am I familiar with advanced inorganic reactions. I will attempt quantum mechanics and thermodynamics questions, but primarily as they relate to biological systems. Furthermore, I cannot tell you if a skin photograph is cancerous, or otherwise diagnose any disease. I can tell you how we currently understand the basic science behind a disease state, but I cannot recommend treatment in any way. Please direct such questions to your medical professional.
Experience
I hold a PhD in Biomedical Science from the University of Massachusetts Medical School in Worcester. I specialize in Biochemistry, with a focus on protein chemistry. My thesis work involved the structure and functions of the human glucose transporter 1. (hGLUT1) Currently I am a postdoc working in peptide (mini-protein) design and enzymology at the University of Texas Health Science Center in San Antonio, Texas. I am in Bjorn Steffensen's lab (PhD, DDS), studying gelatinase A and oral carcinoma.
Organizations
2001 American Association for the Advancement of Science
2007 American Chemical Society
2007 Protein Society
2011 UTHSCSA Women’s Faculty Association
Publications
Levine KB, Robichaud TK, Hamill S, Sultzman LA, Carruthers A. Properties of the human erythrocyte glucose transport protein are determined by cellular context. Biochemistry 44(15):5606-16, 2005. (PMID 15823019)
Robichaud TK, Appleyard AN, Herbert RB, Henderson PJ, Carruthers A “Determinants of ligand binding affinity and cooperativity at the GLUT1 endofacial site” Biochemistry 50(15):3137-48, 2011. (PMID 21384913)
Xu X, Mikhailova M, Chen Z, Pal S, Robichaud TK, Lafer EM, Baber S, Steffensen B. “Peptide from the C-terminal domain of tissue inhibitor of matrix metalloproteinases-2 (TIMP-2) inhibits membrane activation of matrix metalloproteinase-2 (MMP-2)” Matrix Biol. 2011 Sep;30(7-8):404-12. (PMID: 21839835)
Robichaud TK, Steffensen B, Fields GB. Exosite interactions impact matrix metalloproteinase collagen specificities. J Biol Chem. 2011 Oct 28;286(43):37535-42 (PMID: 21896477)
Poster Abstracts:
Robichaud TK, Carruthers. A "Mutagenesis of the Human type 1 glucose transporter exit site: A functional study." ACS 234th Meeting, Boston MA. Division of Biological Chemistry, 2007
Robichaud TK, Bhowmick M, Tokmina-Roszyk D, Fields GB “Synthesis and Analysis of MT1-MMP Peptide Inhibitors” Biological Chemistry Division of the Protein Society Meeting, San Diego CA 2010
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Catalytic Domain Exosites Contribute to Determining Matrix Metalloproteinase Triple Helical Collagen Specificities” Dental Science Symposium. UTHSCSA 2011
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon Research Conference on Matrix Metalloproteinase Biology, Bristol RI 2011
Education/Credentials
Oakland University, Auburn Hills MI BS, Biochemistry 1998
University of Massachusetts Medical School, Worcester MA PhD, Biochemistry & Molecular Pharmacology 2001-2008
University of Texas Health Science Center, San Antonio TX Postdoc, Biochemistry 2009-Present
Awards and Honors
1998 Honors College Graduate, Oakland University
2009 Institutional National Research Service Award, Pathobiology of Occlusive Vascular Disease T32 HL07446
2011 1st Place, Best Postdoctoral Poster, Dental Science Symposium, UTHSCSA, April 2011
Past/Present Clients
Invited Seminars:
Robichaud TK, Fields GB. “Synthesis and Analysis of MTI-MMP Triple Helical Peptide Inhibitors” Pathology Research Conference, University of Texas Health Science Center San Antonio Pathology Department (June 18th, 2010)
Robichaud TK & Hill, B “How To Give A Great Scientific Talk” Invited Lecture, Pathobiology of Occlusive Vascular Disease Seminars, UTHSCSA (Nov 11th 2010), Cardiology Seminar Series, Texas Research Park (Feb 21st, 2011)
Robichaud TK; Tokmina-Roszyk D; Steffensen B and Fields GB “Exosite Interactions Determine Matrix Metalloproteinase Specificities” Gordon-Keenan Research Seminar “Everything You Wanted to Know About Matrix Metalloproteinases But Were Afraid to Ask” Bristol, RI (Aug 6th, 2011)
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