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Exam1reviewnotes - LBS 172 Monday Jan 8th, 2006 Gases...

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LBS 172 Monday Jan 8 th , 2006 Gases Hardest state of matter to see Easiest state to understand at a molecular level Close connection between microscopic behavior and macroscopic properties Molecular Level “Real World” Level *Gas molecules are not in contact (liquid or solid molecules are in contact) * Gases have VERY low density * g/ml or g/cm 3 (D gas << D l or D s ) * Density of gas in g/L * Gases can be used to do WORK *Gas molecules collide with the walls of their container *Gases exert pressure *Gas molecules can collide with each other & these collisions are elastic * (Total Momentum transfer) * Gas molecule = “pool ball” not “silly putty” * simple relationships between pressure (P), volume (V), temperature (T), amount of gas (m) * Gases mix evenly & completely, very rapidly Pressure Pressure = force per unit area N/m 2 = Pa (Pascal) Pascal is too small of a unit so kPa are used kPa = 1000 Pa (kPa = kilo Pascal) 1 atm = 101.5 kPa Atmospheric Pressure at 0˚ C, sea level US Units (lame) – lbs/in 2 = psi 1 atm = 15 psi Barometer Barometer invented by Torricelli The pressure goes down causing the mercury in the barometer to go up Height of the column (Hg) at atmospheric pressure (0˚ C, sea level) = 760 mm Hg 1 atm = 760 mm Hg = 760 torr Relationship between Pressure and Volume As volume decreases (compression) then pressure increases It becomes harder to compress due to pressure increasing Eventually the balloon burst due to overpressure Volume is proportional 1/P – inverse relationship V = k/P therefore PV=K where K = constant for any gas at a specific T

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P i V i = k = P f V f therefore P i V i = P f V f BOYLES LAW Relationship between Volume and Temperature Demonstration = a balloon in liquid N 2 As temperature decreases, volume decrease V is proportional to T – direct relationship V = kT Therefore V/T = k V i /T i = k = V f /T f CHARLES LAW V i /T i = V f /T f Relationship between Volume and n where n = number of moles of gas Demonstration = inflate a balloon As n increases, volume increases V is proportional to n – direct relationship V = kn therefore V/n = k and V i /n i = k = V f /n f o Constant temperature and pressure V i /n i = V i /n i Ideal Gas Law Volume is proportional to 1/P ; Volume is proportional to Temperature ; Volume is proportional to n o Volume is proportional to (nT)/P o Therefore V = (RnT)/P where R = ideal gas constant IDEAL GAS LAW PV = nRT o Ideal = elastic collisions / non-sticky molecules o R = 0.08206 (L∙atm)/(mol∙K) o Must use Kelvin K = ˚C + 273 P x V N/m 2 x m 3 = N x m = WORK! o
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This note was uploaded on 07/25/2008 for the course LBS 172 taught by Professor Laduca during the Spring '08 term at Michigan State University.

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Exam1reviewnotes - LBS 172 Monday Jan 8th, 2006 Gases...

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