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Unformatted text preview: Gas Densities: Examples RT MP d = As the temperature is increased for a given gas at constant pressure, the density decreases The mean molar mass of the atmosphere at the surface of Titan (Satrun’s largest Moon, is 28.6g/mol. The surface temp is 95K and the Pressure is 1.6 atm. Assuming the ideal behavior, calculate the density of Titan’s atmosphere? The mean molar mass of the atmosphere at the surface of Titan (Satrun’s largest Moon, is 28.6g/mol. The surface temp is 95K and the Pressure is 1.6 atm. Assuming the ideal behavior, calculate the density of Titan’s atmosphere? M= 28.6 g/mol P= 1.6 atm T= 95K R= 0.0821 Latm/molK The mean molar mass of the atmosphere at the surface of Titan (Satrun’s largest Moon, is 28.6g/mol. The surface temp is 95K and the Pressure is 1.6 atm. Assuming the ideal behavior, calculate the density of Titan’s atmosphere? M= 28.6 g/mol P= 1.6 atm T= 95K R= 0.0821 Latm/molK RT MP d = d= (28.6 g/mol) (1.6 atm) (0.0821 Latm/molK) (95K) = 5.87g/L Car Safety Air Bags: Example from Text The safety air bags in cars are inflated by nitrogen gas generated by the rapid decomposition of sodium azide: 2 NaN 3 (s) 2 Na(s) + 3 N 2 (g) How many grams of NaN 3 must be decomposed to produce a gas of 36 L at 1.15 atm and 26.0 o C? This problem requires three steps: Step 1: Find the Number of Mols of N 2 Required 1 Step 1: Find the Number of Mols of N 2 Required 1 2 2 7 . 1 ) . 26 1 . 273 )( / 08206 . ( ) 36 )( 15 . 1 ( ) ( N mol K K mol atm L L atm RT PV N n = + − − = = Step 2: Find the Number of Mols of NaN 3 required 2 2 NaN 3 (s) 2 Na(s) + 3 N 2 (g) Step 2: Find the Number of Mols of NaN 3 required 2 2 NaN 3 (s) 2 Na(s) + 3 N 2 (g) 3 2 3 1 . 1 ) 7 . 1 ( 3 2 ) ( 3 2 ) ( NaN mol mol N n NaN n = = ⇒ Step 3: Find the Mass of NaN 3 required 3 Step 3: Find the Mass of NaN 3 required 3 gm mol gm mol nM m 72 )] 14 ( 3 23 )[ 1 . 1 ( = + = = Gas Mixtures and Partial Pressures Dalton’s Law of Partial Pressures: “The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone.” The pressure exerted by a given gas component in a mixture is called the partial pressure of that component. If P t is the total pressure of a gas mixture and P i is the pressure contributed by the ith component, then ... 3 2 1 + + + = P P P P t Each gas component acts independently of the others. Let n t denote the total number of mols of gas and n i be the number of mols of the ith component. V RT n P n n n V RT P n V RT n V RT n V RT P P P P P n V RT P n V RT P n V RT P n n n n t t t t t t = + + + = + + + = + + + = = = = + + + = ...) )( ( ... ) ( ) ( ) ( ... ... ) ( ) ( ) ( ... 3 2 1 3 2 1 3 2 1 3 3 2 2 1 1 3 2 1 The total pressure at constant volume and temperature is determined by the total number of gas molecules whether they are the same or different. Dose this law holds if the gases are reacting ?...
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This note was uploaded on 09/13/2011 for the course CHEM 101 taught by Professor Farahh during the Spring '02 term at UNC.
 Spring '02
 Farahh
 Chemistry, pH

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