2. Gases

3. Exploring Gases Make a table: Demo #PredictionObservation

4. Questions 1.Write the number of the demo that show gases are matter. 2.Write the number of the demo that shows that gases exert pressure.

5. Kinetic Theory Observing Properties of Gases Gases are tiny particles –(Volume assumed to = 0 ) Gases in constant random motion Collisions are elastic Kinetic energy (Movement) depends on temperature No attraction between molecules

6. Measuring Gases Amount (n) moles (number of) Volume (V) liters Temperature (T) Kelvin K= C + 273 Pressure (P) mm Hg or atm

7. Particles colliding with objects Pressure=force (Pascal) area Gas pressure gas particles colliding with objects Atmospheric pressure air particles colliding with objects Pressure

8. Measuring pressure Barometer 760 mm Hg = 1 atmosphere = 101,300 Pascals =14.7 lb/in 2 STP Standard temperature 0oC Standard pressure 1 atm

9. Barometer Measures atmospheric pressure

10. Pressure problems If 760 mm Hg = 1 atm Convert 793 mm Hg to atm Convert 3.5 atm to mm Hg

11. Manometer problems Measures pressure in a closed container

12. Combined Gas law Combines Boyles, Charles, Gay-Lussac law P 1 V 1 = P 2 V 2 T 1 T 2 Calculate in Kelvin!!!!!!!!!!

13. Boyles Law (P,V) At a constant T,N, the volume varies indirectly with the pressure P 1 V 1 = P 2 V 2

14. Charles Law (T,V) At a constant P, N the volume varies directly with the Kelvin temperature V 1 = V 2 T 1 T 2

15. Gay-Lussacs Law (P,T) At a constant V,N the pressure varies directly with the Kelvin temperature. P 1 = P 2 T 1 T 2

16. Dalton’s law The total pressure equals the sum of the partial pressures of the gases in the container P T = P 1 + P 2 + P 3 + ……..

17. Try this Air contains oxygen, nitrogen, carbon dioxide and other gases. What is the pressure due to oxygen in mm Hg if P T = 1 atm P N =593.4 mm Hg P CO2 = 46.78 mm Hg

18. Ideal Gas Law At STP 1 mole=22.4L If not at STP use Ideal Gas Law P V = n R T R=ideal gas constant (0.0821 L atm ) moles K

19. problems The pressure on 2.50 L of anesthetic gas is changed from 765 mm Hg to 304 mm Hg. What is the new volume if the temperature is constant?

20. problems A balloon inflated in air conditioning at 27 o C has a volume of 4.0L. It is heated to 57 o C. What is the new volume?

21. Lab: Boyles Law Purpose: To observe changes in pressure with the volume changes

22. Practice A gas has a volume of 17.3 mL at 3.5 atm. What is the volume if the pressure is increased to 6.7 atm? A can contains a gas at 50 o C and has a volume of.5L. When released what is its new volume at 20 o C?

23. Try this If 87.6 mL of hydrogen gas is collected at a room temperature of 23 o c and room pressure of 742 mmHg, what will the volume be at STP?

24. problems A gas has a volume of 6.8L at 327 o C. What is its volume at 36 o C?

25. Molar Volume 1 Mole = 22.4 L At STP Standard temp 0oC Standard pressure 1 atm

26. Gas Stoichiometry C 8 H 18, octane, combusts in your car’s engine. If the cylinder is 0.500 L and the oxygen intake is at 45 o C and 1.05 atm, how many grams of octane are needed to completely react with the oxygen?

27. Lab: Pressure/temperature Purpose: To determine the absolute zero using Gay-Lussac’s Law

28. Kinetic Theory Gases are made of tiny particles Gases are in constant, rapid motion Gas collisions are elastic Kinetic energy depends on temperature

29. Lab: combined gas law Purpose: To determine the volume of 1 mole of a gas using the combined gas law Reaction: Hydrochloric acid and Mg

30. Assumptions 1.T room = T gas 2.P room = P total 3.All Mg reacts

31. Absolute zero demonstration Temperature at which all molecules stop moving 0 K -273 o C

32. 1. Why should the thistle tube be under the water level? 2.Why was the first bottle “let go”? 3.Why were the bottles placed upside down on the lab bench? 4.What was this method called for collecting gas using a pneumatic trough and pushing water out? 5.Why did the splint go out inside the bottle? 6.What was the clear, colorless liquid produced? 7. Write a chemical reaction for its production.

33. Lab: Combined gas law 1.Take room temperature and pressure 2. Get about 5 cm (or less) Mg and mass. Tie onto copper wire 3. Pour 15 ml of HCl into eudiometer and fill to top with water 4. Put Mg into top of eudiometer. Stopper. 5. Put finger over the hole, turn upside down and place into big beaker of water. 6. When reaction is complete, put finger over hole and transfer to large graduated cylinder to measure volume of gas collected.