# The Empirical Gas Laws Avogadros Law : Equal volumes of any two gases at the same temperature and pressure contain the same number of molecules. The volume.

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The Empirical Gas Laws Avogadros Law : Equal volumes of any two gases at the same temperature and pressure contain the same number of molecules. The volume of one mole of gas is called the molar gas volume, V m. Volumes of gases are often compared at standard temperature and pressure (STP), chosen to be 0 o C and 1 atm pressure.

Avogadros Law (See Animation: Pressure and Concentration) Go to 7 At STP,

The Ideal Gas Law The constant is independent of temperature, pressure but does depend on amount of the gas The constant is independent of temperature, pressure and amount of the gas Ideal gas law

The Ideal Gas Law and the Molar Gas Constant For one mole of a gas at STP (P = 1atm, T=273K)

Using the Ideal Gas Law Haw many grams of oxygen are there in a 50.0 L gas cylinder at 21 C when the oxygen pressure is 15.7 atm? atmLmol K = C + 273 0.082

Gas Density from Ideal Gas Law What is the density of O 2 (in g/L) at 25 C and 0.850 atm? V = 1L ; P = 0.850 atm, T = (25+273)K = 298 K Using the ideal gas law, we can calculate n then we can calculate the density d (of O 2 at 25 C and 0.85 atm ) = 1.11 g/L

Gas Density and Molar Mass Determination Density of gasMolar mass of gas

An Example What is the density of O 2 (in g/L) at 25 C and 0.850 atm? Similarly, we can calculate M if we know d Density of gasMolar mass of gas

Stoichiometry Problems Involving Gas Volumes Use the ideal gas law Example Air bags are inflated upon collision with N 2 gas using The following fast reaction: ? g of NaN 3 are required to provide 75.0 L of N 2, at 25 C and 748 mmHg

Answer Use the ideal gas law ? mol of NaN 3 = 3.02 6/9 = 2.01 mol NaN 3 ? g of NaN 3 = 2.01 (mol NaN 3 ) 65.01 (g/mol) NaN 3 =131 g NaN 3 3.02 mol 75.0 L ? mol 6 moles 9 moles

Partial Pressures of Gas Mixtures Daltons Law of Partial Pressures: the sum of all the pressures of all the different gases in a mixture equals the total pressure of the mixture. Where each gas in the mixture obeys the ideal gas law

A gas Mixture and Daltons Law of Partial Pressures PP ti i N 1 ; i = 1,2,3,…..N The gas mixture as well as each individual gas in the mixtureoccupies the same volume andobeys the idealgas law, where PVnRT tt PVnRT ii ; i = 1,2,3,…..N P P n n i t i t i i t n n (mole fraction) PP iit

Example 1.00 L of dry air at 25 C and 786 mmHg contains 0.925 g N 2 + other gases b. What is the mole fraction of N 2 in air? c. What is the mole percent of N 2 in air?

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