Pressure Partial Pressure Gas Stoichiometry

1. PressurePartial PressureGas Stoichiometry Pressure = Force/Area Dalton’s Law of Partial Pressures Avogadro’s Law

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

3. 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?

4. 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

5. Volume MEasurements • Boxes = length x width x height • Cylinders = pi x diameter x height

6. 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

7. 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

8. 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/m2 • 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 0oC

9. Standard Temperature and Pressure • STP • Comparing conditions at 1 atm and 0oC

10. Unit conversions • 1 atm = • 760 mm Hg = • 760 torr = • 1.013 x 105 Pa = • 101.3kPa 1atm 760 mm Hg 760 torr 101.3kPa 101.3kPa 101.3kPa 760 mm Hg 1.013 x 105 Pa 760 torr 1.013 x 105 Pa 1.013 x 105 Pa 1atm 1atm 760 torr

11. 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

12. Dalton’s Law of Partial Pressures • Pressuretotal = PressureA + PressureB

13. Finding Partial Pressures • PressureA = Pressuretotal - PressureB

14. 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

15. Stoichiometry of Gases • What do we already know about stoichiometry? • Using chemical equations to know the ratios between different compounds • N2H4 + 2H2O2 -> N2 + 4H2O • 1 mol N2H4 for 2 mol H2O2 • 1 mol N2H4 for 1 mol N2 • 1 mol N2H4 for 4 mol H2O • 2 mol H2O2 for 1 mol N2 • 2 mol H2O2 for 4 mol H2O • 1 mol N2 for 4 mol H2O

16. Avogadro’s Law • “equal volumes of gases at the same temperature and pressure contain equal numbers of molecules”\ • What does this mean? • H2(g) + Cl2(g) -> 2HCl(g) • 1 mol H2 = 1 mol Cl2 = 2 mol HCl • 1 molecule H2 = 1 molecule Cl2 = 2 molecules HCl • 1 Volume H2 = 1 volume Cl2 = 1 volumeHCl

17. 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

18. 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?