DALTONsolved

# DALTONsolved - More About Pressure "This world is rough,...

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“This world is rough, and if a man’s gonna make it, he’s gotta be tough” – Johnny Cash – A Boy Named Sue DALTON’S LAW OF PARTIAL PRESSURE Dalton’s Law P = n total RT V n total = n molecule1 + n molecule2 + n molecule3 P = (n molecule1 + n molecule2 + …) RT V therefore, P total = (n molecule1 )RT + (n molecule2 )RT + … V V p molecule1 p molecule2 called partial pressures P total = p molecule1 + p molecule2 + etc. p molecule”n” = n molelecule”n” (RT/V) = n moleule”n” = X n P total n total (RT/V) n total X n is called mole fraction of molecule n Example During the deposition of a thin film of the semiconductor GaAs on a surface at high temperature, hydrogen is generated according to the following balanced equation: AsH 3 ( g ) + GaH 3 ( g ) GaAs ( s) + 3H 2 ( g ) The reaction is carried out with AsH 3 and a slight excess of GaH 3 . 835 mL of hydrogen gas was collected over water at 30.0 o C at a barometric pressure of 734 mmHg. [MM (g/mol): AsH 3 = 77.95; GaH 3 = 72.74] How many grams of AsH 3 were consumed? (You may assume the mixture collected contains only H 2 O vapor and H 2 gas.) P T = P H2 + P H2O ; 734 mmHg = P H2 + 31.82 mmHg ; P H2 = 702.18 mmHg n H2 = (PV)/(RT) = (702.18/760) (0.825)/(0.8206)(30 + 273.15) = 0.0306258 moles H 2 [0.0306258 moles H 2 ][1 AsH 3 / 3 H 2 ][77.95 g/mol] = 0.796 g What is the mole fraction of water in the gas mixture? (Same assumption.) X H2O = n H2O /(n H2O + n H2 ) = n H2O /(n H2O + 0.0306258) n H2O = (PV)/(RT) = (31.82 / 760 )(0.825) / (0.08206)(30 + 273.15) = 0.0013878

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## This note was uploaded on 04/12/2008 for the course CHEM 109 taught by Professor Malina during the Spring '08 term at UNL.

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DALTONsolved - More About Pressure "This world is rough,...

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