Chem 112 Exam AID Course Pack

# E making the approximation of an ideal gas more

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Unformatted text preview: approximation (infinite high temperature and molecules infinitely far apart) The 3 Gas Laws: 1.Avogadro’s Law: –At a given T and P, different gases in a volume have the same number of moles V= Constant * n 2.Boyle’s Law –P1V1 = P2V2 3.Charles's Law –The volume of a gas is directly proportional to its absolute temperature –V=constant * T The Ideal Gas Law states that PV = nRT. P = pressure (kPa), V = volume (L), n = number of moles, R = the Universal Gas Constant (8.31 kPa L K- 1 mol - 1), T = temperature (K). (Note the units) This is your basic equation for understanding gases. In fact, you can get all the other gas laws from it: - Given constant n, R, T, increasing pressure will decrease volume, and vice versa, or PV=nRT won’t be true (Boyle’s Law: P1V1 = P2V2). - Given constant n, R, V, increasing pressure will increase temperature, and vice versa, or PV=nRT won’t be true (Amontons’ Law: P1/T1 = P2/T2) (again, temperature in K) Ethan Newton & Barry Zhang for SOS Winter 2012 16 - Given constant n, R, P, increasing temperature will increase volume, and vice versa, or PV=nRT won’t be true (Charles’s Law: V1/T1 = V2/T2) If you don’t want to bother with which one(s) to use, apply the Combined Gas Law instead: P1V1/T1 = P2V2/T2, which gives you the above three laws all put into one. If the mass of gas changes, there is an even more general form, P1V1/n1T1 = P2V2/n2T2 What is the relationship between V and n, with the other quantities constant? (Avogadro’s Law) PV=nRT doesn’t say anything about multiple types of molecules, so long as the gas is still ideal; it only talks about number of molecules. Therefore, it applies to both the total number of molecules and the number of molecules for any individual gas (and you get Dalton’s Law and Raoult’s Law). Each gas exerts pressure independently, so PT = P1 + P2 + ...+ Pn and PA = xAPT. As a direct consequence of this, PA = xAPT. Since all of these are essentially applications of the Ideal Gas Law, they get less accurate as the ideal gas approximation becomes less accurate. Density: ρ = m/V - m can be calculated from n (and molecular masses) - the SI units of density are the cubic meter; but we use the cubic decimetre (also called the litre, L) as a more convenient measurement Pressure: P = F/A, where F is in Newton’s and A is in square meters. - the SI units of this are in N/m2, or Pascals (Pa) - pressure is essentially equivalent at all points of the container - note that if a gas is exerting a certain pressure,...
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