Gas lawscheat sheet


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Gas lawscheat sheet

  1. 1. High School Chemistry - Core Concept Cheat Sheet 18: Gas Laws Key Gas Law Terms Attacking Strategy for Gas Laws:  Kinetic Molecular Theory (KMT): The theory of moving molecules to explain gas behavior with a set of postulates.  Kelvin (K): Temperature scale used in gas calculations. It has an absolute zero. C + 273.15 = K  Pressure: Force of gas molecules colliding with surfaces.  Atmospheric Pressure: Pressure due to the layers of air in the atmosphere.  Standard Temperature and Pressure (STP): 1 atm (or anything it’s equal to) and 0C (273.15 K).  Dalton’s Law of Partial Pressure: The total pressure is the sum of each type of gas’s pressure.  Mole Fraction (): The ratio of moles of a specific molecule to the total number of moles.  Ideal Gas: All assumptions of the kinetic molecular theory are true.  Real Gas: The assumptions that molecules have no attractions/repulsions and that the particle volume is insignificant are not valid.  Molar Volume of a Gas: 1 mole of any gas at STP = 22.4 Liters. 1. 2. 3. Identify quantities by their units. Write known and unknown quantities symbolically. Choose equation to apply based upon list of quantities. Convert Units, Plug Quantities into Equation and Solve the Gas Laws Symbols for all gas Laws: P = Pressure V = Volume n = moles T = Temperature (in Kelvin) R = Gas constant 8.31 L  kPa mole  K Dimensional analysis can be used to convert between them. Kinetic Molecular Theory Assumptions of the KMT 1. Gases are made of atoms or molecules. 2. Gas particles are in rapid, random and constant motion. 3. The temperature is proportional to the average kinetic energy. 4. Gas particles are neither attracted nor repelled from each other. 5. All gas particle collisions are perfectly elastic. They leave with the same energy they collided with. 6. The volume of gas particles is so small compared to the space between them that the volume of the particle is insignificant. Average Kinetic Energy = (3/2)RT where R = 8.31 Jk-1•mol-1 Relationships between Gas Properties The Ideal Gas Law: PV = nRT # of molecules and pressure: Directly proportional, nP. Pressure and volume: Inversely proportional, P1/V. Pressure and temperature: Directly proportional, PT. Combined Gas Law:  Atmospheric pressure decreases as altitude increases.  Containers contract to pressure. o o (soft or with a moveable piston) expand or allow internal pressure to equal external Expansion lowers internal pressure. Contraction raises internal pressure.  Rigid container cannot expand or contract—they will explode or implode. L  atm mole  K P1V1 P2V2  n1T1 n2T2 When something is held constant, the value is the same on both sides and it is cancelled out.  Avogadro’s Law: Hold Pressure and Temperature constant. V1/n1 = V2/n2  Boyle’s Law: Hold moles and Temperature constant (The last letter of his first name, RoberT, is T). P1V1 = P2V2  Charles’ Law: Hold moles and pressure constant (He was from Paris). V1/T1 = V2/T2 Gas Laws Rhyme: Avogadro - hold P, T; Bolyes - hold T; Charles - hold P = “ABC – PreTend To Pee!” Dalton’s Law of Partial Pressure: Mole fraction: A  Ptotal   Pof each gas mole A moletotal Partial Pressure and mole fraction: PA   A Ptotal Ideal Gas Law: PV  nRT Mnemonic: “Phony Vampires Are(=) not Real Things!” Density with Ideal Gas Law: P = DRT/MM Real Gas Law: Pressure Inside and Outside 0.0821 “a” and “b” = correction factors for real gases Pressure Units 1 atm = 101300 Pa = 101.3 kPa = 760 mm Hg = 14.7 psi or  n2a   P  2 V  nb   nRT  V    Gas Stoichiometry STP Stoichiometry  Use 1 mole = 22.4 L as an equivalent in the stoichiometry to find volume of the gas at STP. Non-STP  Use stoichiometry to find the STP volume of the gas  Then use a gas law to convert to desired temperature and/or pressure if the question asks for non-STP conditions. How to Use This Cheat Sheet: These are the keys related to this topic. Try to read through it carefully twice then recite it out on a blank sheet of paper. Review it again before the exams.  Rapid Learning Inc. All Rights Reserved