Pressure Partial Pressure Gas Stoichiometry Pressure = Force/Area Dalton’s Law of Partial Pressures Avogadro’s Law

What do we already know? Kinetic Molecular Theory –5 assumptions No definite shape, no definite volume Expansion, diffusion, compressibility

Question By the end of the lecture try to answer the question: At the same temperature and volume, why do larger gas molecules exert more pressure on their container?

VOlume Gas particles will take on the volume of the container they are in To measure the volume of the gas, measure the volume of the container it is in

Volume MEasurements Boxes = length x width x height Cylinders = pi x diameter x height

Pressure Pressure is the force exerted over an area Force is measured in Newtons (N) The Force of gas particles is created by the moving gas particles hitting the sides of their container

Measuring Pressure Pressure is measured with a barometer The first barometer measured pressure by measuring how high a gas could raise a column of mercury, thus the units of pressure were: –mm of Hg

Units of Pressure Like there are different ways to measure weight or length, there are different ways to measure pressure Torr is equal to 1 mm of Hg The SI unit for pressure is Pascal (Pa) –1 pascal = 1 N/m 2 –The kilopascal (kPa) is also used The most widely used unit is the atmosphere (atm) it is the average atmospheric pressure at sea level and 0 o C

Standard Temperature and Pressure STP Comparing conditions at 1 atm and 0 o C

Unit conversions 1 atm = –760 mm Hg = –760 torr = –1.013 x 10 5 Pa = –101.3kPa 1atm760 mm Hg760 torr x 10 5 Pa 101.3kPa 760 mm Hg101.3kPa x 10 5 Pa 760 torr 1atm x 10 5 Pa 101.3kPa

Dalton’s Law of Partial Pressures “The total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases” What does this mean? Remember that we assume that gas molecules are not affected by each other Therefore, each type of molecule will act independently of any other type To find the total pressure, we just add the pressures of the individual types of molecules together

Dalton’s Law of Partial Pressures Pressure total = Pressure A + Pressure B

Finding Partial Pressures Pressure A = Pressure total - Pressure B

Partial Pressures Last Comments Partial pressures must be in the same units to be compared The number of pressures in a mixture does not affect the Dalton’s law of partial pressures equation

Stoichiometry of Gases What do we already know about stoichiometry? Using chemical equations to know the ratios between different compounds N 2 H 4 + 2H 2 O 2 -> N 2 + 4H 2 O 1 mol N 2 H 4 for 2 mol H 2 O 2 1 mol N 2 H 4 for 1 mol N 2 1 mol N 2 H 4 for 4 mol H 2 O 2 mol H 2 O 2 for 1 mol N 2 2 mol H 2 O 2 for 4 mol H 2 O 1 mol N 2 for 4 mol H 2 O

Avogadro’s Law “equal volumes of gases at the same temperature and pressure contain equal numbers of molecules”\ What does this mean? H 2 (g)+ Cl 2 (g) -> 2HCl(g) –1 mol H 2 =1 mol Cl 2 =2 mol HCl –1 molecule H 2 = 1 molecule Cl 2 =2 molecules HCl –1 Volume H 2 = 1 volume Cl 2 = 1 volumeHCl

Standard Molar Volume “the volume occupied by 1 mol of a gas at STP” What does this mean? –At standard temperature and pressure (STP) 1 mol of gas will always occupy the same volume 22.4 L / 1 mol at STP This is a conversion factor you have seen before

Review Pressure is Force over area The partial pressures of a mixture of gases are added together to form the total pressure of the mixture Avogadro’s law compares mols, volumes, and molecules of gases in a balanced chemical equation At STP, 1 mol of gas occupies 22.4 L At the same temperature and volume, why do larger gas molecules exert more pressure on their container?