Chapter 5 Overall Notes
Chapter 5 Overall Notes CHEM 1307
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This 4 page Class Notes was uploaded by Kyle A. Headen on Tuesday October 11, 2016. The Class Notes belongs to CHEM 1307 at Texas Tech University taught by Tamara Hanna in Fall. Since its upload, it has received 8 views. For similar materials see /class/226511/chem-1307-texas-tech-university in Chemistry at Texas Tech University.
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Date Created: 10/11/16
Chapter 5 Pressure: The United States National Institute of Standards and Technology uses one atmosphere as the standard pressure. Pressure is force per unit area. The S. I. unit of force is the newton. Force = mass x acceleration 1 newton = 1 kg m s-2 The S. I. unit of pressure is the pascal. 1 pascal (Pa) = 1 newton / meter2 1 pascal = 1 kg m s-2m-2 = 1 kg s-2m-1 1 bar = 1 x 105 pascals (Pa) 1 bar = 100 kilopascals (kPa) 1 bar = 1 x 105 kg s-2m-1 1 bar = 0.9872 atmospheres 1 atmosphere = 760 mm Hg = 760 torr 1 atmosphere = 14.6960 pounds per square inch 1 atmosphere = 1.01325 bar 1 atmosphere = 1.01325 x 10^5pascals Memorize the following conversion factor: 1 atmosphere = 760 mm Hg = 760 torr General Gas Law: P1V1/(T1) = P2V2/(T2) This equation can be used for any problem in which the amount (number of moles) of gas stays the same. If any variable (P, V, or T) stays the same, it can be cancelled from both sides, and the equation is then reduced to Boyle’s, Charles’s, or Gay-Lussac’s Law. P V = n R T R is the ideal gas constant. R = 0.082057 L atm K-1mol-1 R = 8.314472 J K-1mol-1 Note that Liters x atmospheres (V x P) are units of energy in the form of work. PV Work: Work is done when a gas undergoes a volume change at constant pressure. Work = P*Delta V Pressure is force per unit area. Force = mass x acceleration = (kg) (m s-2) Pressure = force / area = (kg m s-2) / m2 = kg m-1 s-2 Pressure x Volume = (kg m-1 s-2) (m3) = kg m2 s-2 Work = Force x displacement = (kg m s-2) (m) = kg m2 s-2 Remember that kg m2 s-2 are units of energy (Joules). Compare to the formula for kinetic energy: Kinetic Energy = ½ m v2 Energy units are kg (m s-1)2 = kg m2 s-2= 1 Joule Standard Condition: Many physical properties of gases are listedin tables of data. In order to be able to compare values for different gases,the values are given for gases that are at the same temperature and pressure. Standard temperature for gases is 0oC (273.15 K) Standard pressure for gases is 1atm. Gas Densityand Molar Mass: n (# of moles) = (mass) / (molar mass) ‘P V = n R T P V = (m / M) R T This equation can be used to determine the molar mass (M) of a gas if the pressure, volume, P V = (m / M) R Tture are known. The equation can be rearranged to show the relationship between the density of a gas and the other variables. density= m = ( )( ) V R T ( )( ) To calculate Molar Mass: P M density= m = ( )( ) V ( )( ) (m)(R)(T) density R (T) M (V)(P) P Gas Mixtures and Partial Pressures: In a mixture of ideal gases there is no force of attraction between any of the gas molecules. Each gas in the mixture behaves independently of all the others and obeys the ideal gas law. PA = nA PB = nB R T / V; etc.A, B, C,… in a container of volume V: The total pressure of the gas mixture is equal to the sum of all of the “partial pressures” of the components (A, B, C, …) in the mixture. Ptotal = PA + PB + PC + … Since PA = nA R T / V; PB = nB R T / V; etc. Ptotal = PA + PB + PC + … Ptotal = (nA + nB + nC + …) (R T / V) Ptotal = (ntotal) (R T / V) The mole fraction of each gas in the mixture is the number of moles of that gas divided by the total number of moles of all of the gases in the mixture. XA = nA / (nA + nB + nC + …) = nA / ntotal nA = (XA) (ntotal) The partial pressure of gas A is therefore: PA = XA Ptotal The Kinetic-Molecular Theory of Gases: kinetic energy = ½ m u2 where u is the speed of the molecule. average kinetic energy = ½ m ù2 where ù2 is the average of the squares of the speeds of the molecules. From experiment, it is known that: average kinetic energy = (3/2) R T When using this formula, make sure that R has units of energy (joules). R = 8.314472 J K-1mol-1
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