Gases Chapter 1 Ron Robertson a c:\files\courses\3610\ch1trans.docGases Slide 1 Overview I. What is physical chemistry? II. Some meanings of the term state III. Kinetic theory and the ideal gas IV. Real gases for real peopleGases Slide 2 I. What is physical chemistry? A. The study of the underlying principles that govern the behavior of chemical systems B. 2 views microscopic - use of molecules macroscopic - large scale properties without the use of molecules C. Areas Thermodynamics - relationships among the various equilibrium properties of a system Quantum mechanics - new set of laws which govern motions of molecules, atoms, electrons and nuclei. The study of spectroscopy is derived from this.Gases Slide 3 Statistical mechanics - relates the macroscopic to the microscopic. Allows the calculation of macro properties form the micro. Kinetics - study of reaction rate, uses parts of thermo, quantum mechanics and stat mechGases Slide 4 II. Some meanings of the term state A. States of matter (solid, liquid, gas) or B. A description of a sample of matter in terms of macroscopic variables V, P, T and n 1. volume - m3, ft3, liters, ml 2. pressure (Force/area) direct lb/in2, N/m2 or Pa, bar (1 bar = 105 Pa) indirect Atmosphere, mm Hg or torr, in of Hg Conversions Old Standard Pressure 14.7 lb/in2 760. mm Hg or torr 101.3 kPa 1.013 bar 1.00 Atm 29.9 in of Hg New definition of standard pressure is exactly 1 barGases Slide 5 3. Temperature - measure of average KE Gives an indication of energy flow - no energy flow means thermal equilibrium (same temp) Celsius Fahrenheit Kelvin Rankine K = C + 273 R = F + 460. C = 5/9 (F -32) F = 9/5 C + 32 4. Number of particles - the mole 1 mole = 6.02 x 1023 particles allows conversions g moles moleculesGases Slide 6 C. Equations of state 1. V, P, T and n are not independent Once we specify 3 - the other is already determined. The equation of state relates these variables 2. The equation of state is not known for most substances because of complicated interactions but the equation for low pressure gases is.Gases Slide 7 III. Kinetic Theory and the Ideal gas law A. Assumptions Matter made of particles Particles are in constant motion Particles collide elastically unless they react All particles of the same substance and at the same temperature don’t have the same kinetic energy B. Ideal gas - particles are very far apart and their size is negligible compared to the distance they travel between collisions C. Equation of state for an ideal gas Boyle’s Law Pressure and volume are inversely proportional provided temperature and number of particles are held constant.Gases Slide 8 Charles’ Law Volume and temperature are directly proportional provided pressure and the number of particles are held constant Avogadro’s principle At same T and P equal volumes of gases contain equal numbers of particles. D. Ideal or perfect gas law PV = nRT Equation of state DPMRT D = density R is the gas constant (8.314 J/mole K or kPa-L/ mole K ; 62.4 L-Torr/mole K; 0.0821atm L/mole k)Gases Slide 9 If the conditions of the gas change then PPVVnnTT12121212 E. Dalton’s Law of Partial Pressures Total pressure is the sum of partial pressures PT = PA + PB + PC + . . . . but VT = VA = VB = VC and nT = ? Derive to get PT = XA PT + XBPT + XCPT + . . . where XA = nA/ nT the mole fraction This of course means that PA must equal