CH131_4B

CH131_4B - We can use the ideal gas law for some...

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We can use the ideal gas law for some quantitative descriptions of chemical reactions involving gas reactants and/or products. For example: consider the thermal decomposition of ammonium nitrite => NH 4 NO 2 (s) N 2 (g) + 2H 2 O(g) (balanced) Suppose 2.55 g of NH 4 NO 2 (s) is heated in a 1.00 L container to 101 o C. What pressure of N 2 (g) is generated in the container? Solution strategy: PV = nRT => P N 2 = n N 2 RT V All known except n N2 Determine n N2 from stoichiometry (1 mol N 2 from 1 mol NH 4 NO 2 ) # mols NH 4 NO 2 = 2.55 g 1 mol NH 4 NO 2 64.0 g = 0.0398 mol NH 4 NO 2 # mols N 2 = 0.0398 mol NH 4 NO 2 1 mol N 2 1 molNH 4 NO 2 = 0.0398 mol N 2
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P N 2 = n N 2 RT V = 0.0398 mol N 2 0.0821 L atm K - 1 mol ( ) 101+ 273 K ( ) 1.00 L =1.22 atm OK; but for this reaction, for example, 2 gases are formed: NH 4 NO 2 (s) N 2 (g) + 2H 2 O(g) So, what is the total pressure formed from the mixture of these 2 products gases? In the spirit of the ideal gas law (gases are mostly empty space; all intermolecular interactions are neglected) => assume ideal gas law applies to all components in a gas mixture (each gas component ignorant of the presence of the other gases!) Thus for a mixture of m gases we have (note RT/V is a constant): P 1 = n 1 RT V ; P 2 = n 2 RT V ; ...... ; P m = n m RT V ; Total P = P Tot = P 1 + P 2 + .... P m = n 1 + n 2 + .... + n m ( ) RT V P m partial pressure of species m
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Total P = P Tot = P 1 + P 2 + .... P m = n 1 + n 2 +.... + n m ( ) RT V P Tot = n Tot RT V where n Tot = n 1 + n 2 + .... + n m ( ) This sentence is called Dalton’s Law: Total P = sum of partial P each gas in a mixture exerts a P as if it were the only component present. P of N
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This note was uploaded on 04/17/2008 for the course CAS CH131 taught by Professor Zigler during the Spring '08 term at BU.

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CH131_4B - We can use the ideal gas law for some...

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