Ch_05b - The Ideal Gas Law PV = constant = R nT (An ideal...

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24 P in atm, V in L, n in moles, T in kelvins. • If any other units are used for these variables, a different value for R must be used … Å The ideal gas law PV = nRT The Ideal Gas Law For 1 mol of an ideal gas at STP … R = 0.08206 L atm mol –1 K –1 (ideal gas constant) R constant = = nT PV (An ideal gas strictly obeys all the gas laws, and has a molar volume at STP of 22.4141 L.) 25 Units for the Gas Constant, R All units are “energy per mol per Kelvin” Joules (J) is the energy unit most frequently encountered ; V is in L ; V is in L An ideal gas is a hypothetical gas; • Real gases approximate ideal gas behavior at low P and high T . • Real gases (high P , low T ) depart seriously from ideal gas behavior.
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26 What is the volume occupied by 16.0 g ethane gas (C 2 H 6 ) at 720 Torr and 18 o C? 6 2 6 2 6 2 6 2 H C mol 532 . 0 H C g 07 . 30 H C mol 1 H C g 0 . 16 = × = n K 291.15 K ) 18 15 . 273 ( = + = T atm 947 . 0 Torr 760 atm 1 Torr 720 = × = P L 4 . 13 atm 0.947 K 291.15 K mol atm L 0.0821 mol 532 . 0 -1 -1 = × × = = P nRT V 27 Application of Gas Laws
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28 Molecular Mass Determination The molar mass of a gas can be determined using the ideal gas law … Given M = molar mass, and m = mass in grams M ×n = m (in grams) or n = m / M Finally, PV = nRT becomes RT M m PV = PV mRT M = 29 What is the molar mass of a gas if 23.6 g exerts a pressure of 1293 torr at 37.0 o C in a 17.5-L container? P = 1293 torr × 1 atm 760 torr = 1.7013 atm V = 17.5 L T = 37.0 + 273.15 = 310.15 K PV = nRT n = PV RT = 1.7013 atm × 17.5 L 0.08206 L atm mol -1 K -1 × 310.15 K = 1.17 mol m = 23.6 g M = m / n = 1.17 mol 23.6 g = 20.2 g/mol The gas could be Ne.
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30 Calculate the molecular mass of a liquid that, when 0.523 g is
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This note was uploaded on 05/06/2008 for the course CHEM 103 taught by Professor Forgot during the Spring '07 term at CUNY City.

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Ch_05b - The Ideal Gas Law PV = constant = R nT (An ideal...

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