1. Gases Gases

2. Kinetic Theory of Gases A gas consists of small particles that move rapidly in straight lines. have essentially no attractive (or repulsive) forces. are very far apart. have very small volumes compared to the volume of the container they occupy. have kinetic energies that increase with an increase in temperature.

3. Properties That Describe a Gas Gases are described in terms of four properties: pressure (P), volume(V), temperature(T), and amount(n).

4. Gas Pressure Gas pressure is described as a force acting on a specific area. Pressure (P) = Force Area Has units of atm, mm Hg, torr, lb/in. 2 and kilopascals(kPa). 1 atm = 760 mm Hg (exact) 1 atm = 760 torr 1 atm = 14.7 lb/in. 2 1 atm = 101.325 kPa 1atm = 1013 millbars

5. Closed End Manometer Reading Closed End Manometer Direct read instrument Height(h) is the mmHg pressure of the gas in the bulb (ALWAYS).

6. Open End Manometer Reading Open End Manometer Atmosphere vs. gas Higher pressure is down Distance between Hg levels is the difference between the the pressure of the two sides “There is a Battle going on”

7. Learning Check A. What is 475 mm Hg expressed in atm? 1) 475 atm 2) 0.625 atm 3) 3.61 x 10 5 atm 475 mm Hg x 1 atm = 0.625 atm 760 mm Hg

8. Learning Check B. The pressure in a tire is 2.00 atm. What is this pressure in mm Hg? 1) 2.00 mm Hg 2) 1520 mm Hg 3) 22 300 mm Hg 2.00 atm x 760 mm Hg = 1520 mm Hg 1 atm

9. Atmospheric Pressure Atmospheric pressure is the pressure exerted by a column of air from the top of the atmosphere to the surface of the Earth.

10. Altitude and Atmospheric Pressure Atmospheric pressure is about 1 ATM (atmosphere) at sea level. depends on the altitude and the weather. is lower at high altitudes where the density of air is less. is high for sunny and low for cloudy and rainy conditions

11. Barometer & Barometric pressure A barometer measures the pressure exerted by the gases in the atmosphere. indicates atmospheric pressure as the height in mm of the mercury column.

12. Dalton’s Law P t = p x + p y + p z …. Pressure total is the sum of all of the individual gas pressures(partial pressure) in a container The pressure of one gas does not affect the pressure of other gases. Could be more than 3 gases.

13. Vapor Pressure of Water Vapor pressure of water is the pressure of the gas molecules above the liquid surface at a given temperature. Higher temperature means more molecules leave the surface and HIGHER pressure.

14. What is the Nitrogen pressure when caught over water at 22°C with a total pressure of.5Atm. At 22°C, Vapor pressure (H2O) = 19.8mmHg P t =.5 Atm = 380 mmHg (Use DA) Using Dalton’s formula P t = pN 2 + pH 2 0 380mmHg = pN 2 + 19.8mmHg pN2 = 360.2mmHg

15. Pressure and Volume (Boyle’s Law)

16. Boyle’s Law Boyle’s Law states that the pressure of a gas is INDIRECTLY related to its volume when T and n are constant. if volume decreases, the pressure increases P 1 *V 1 =P 2 *V 2

17. Learning Check If a sample of helium gas has a volume of 120 mL and a pressure of 850 mm Hg, what is the new volume if the pressure is changed to 425 mm Hg ? 1) 60 mL 2) 120 mL3) 240 mL Known:P 1 = 850 mm HgP 2 = 425 mm Hg V 1 = 120 mLV 2 = ?? P 1 V 1 =P 2 V 2 V 2 = V 1 x P 1 = 120 mL x 850 mm Hg = 240 mL P 2 425 mm Hg Pressure ratio increases volume

18. P or V changes if H2O is present

19. Multiple Cylinder Problem

21. Temperature and Volume (Charles’ Law) Copyright © 2005 by Pearson Education, Inc. Publishing as Benjamin Cummings

22. Charles’ Law In Charles’ Law, the Kelvin temperature scale MUST be used in Gas Las relationships K = °C + 273 P and n are constant. Direct relationship: when the temperature of a gas increases, its volume increases. V 1 /T 1 =V 2 /T 2

23. Calculations: Charles’ Law A balloon has a volume of 785 mL at 21°C. If the temperature drops to 0°C, what is the new volume of the balloon (P constant)? Be sure to use the Kelvin (K) temperature in gas calculations. 1.Set up data table: Conditions 1Conditions 2 V 1 = 785 mLV 2 = ? T 1 = 21°C = 294 KT 2 = 0°C = 273 K

24. Calculations: Charles’ Law 2. Solve Charles’ law for V 2 : V 1 = V 2 T 1 T 2 V 2 = V 1 x T 2 T 1 V 2 = 785 mL x 273 K = 729 mL 294 K

25. Mole Fraction Formula

26. Ideal Gas Law Calculations

27. Sample New Molar Volume

28. Molar Volume of Hydrogen Gas Lab Mass of Mg Ribbon: 1.1g/meter Length of Mg Ribbon: 2cm Barometric Pressure: 30.27inches Temperature: 23˚C Volume of wet H 2 measured in tall cylinder as shown below: 22.5ml Causes pressure equilization