2. Combined Gas Law Agenda Demos & Notes on gas laws Homework: Gas Laws

3. Combined Gas Law Date:

4. Kinetic Molecular Theory The theory that a gas consists of molecules in constant random motion.

5. Postulate 1 Gases are composed of molecules whose size is negligible compared with the average distance between them.

6. Postulate 2 Molecules move randomly in straight lines in all directions and at various speeds. Pressure is the same in all directions Changes directions when it collides

7. Postulate 3 The forces of attraction or repulsion between two molecules in a gas are very weak or negligible, except when they collide.

8. Postulate 4 When molecules collide with one another, the collisions are elastic.

9. Postulate 5 The average kinetic energy of a molecule is proportional to the absolute temperature.

10. Variables P: pressure V: volume T: temperature – must be in Kelvin Celsius, o C and Kelvin o C + 273 = K

11. Pressure Force exerted per unit of area Has multiple units: psi, kg/ms 2 = pascal, mmHg = torr, atm. Evagelista Torricelli created the mercury barometer

12. Standard Pressure 1 atm = 760 torr = 760 mmHg = 101.3 kPa Convert between units using std pressures as conversion factors.

13. Temperature Measure of the average kinetic energy of the molecules.

14. Volume The space occupied by matter For which state of matter can the volume be changed simply by changing the pressure or temperature?

15. What does a vacuum pump do? Decreases the pressure by removing air molecules

16. Observe the balloon and marshmallow. What is the relationship between pressure and volume?

17. Modified Volcano Vinegar and baking soda make CO 2. As more MC of gas are created, pressure increases and it needs more volume. Stopper blows

18. Boyles Law P 1 V 1 = P 2 V 2 Pressure varies inversely with volume.

19. This little light of mine Flame burning = high T, MC moving fast = high P and take up more space. Cover with graduated cylinder, use up all O 2 flame goes out instantly reducing T. Less movement, less pressure. Atm forces liquid up!

20. Gay – Lussac Law P 1 T 2 = P 2 T 1 Pressure varies directly with temperature. Temperature MUST be in Kelvin and is not used to determine SF.

21. Hand Warmer Cold jar, balloon deflated Warm jar, increase T, volume of balloon increases.

22. Charles Law V 1 T 2 = V 2 T 1 Volume varies directly with temperature. Temperature MUST be in Kelvin and is not used to determine SF.

23. Fountain Increase pressure in container, by decreasing space between gas molecules. Stop blowing, releases pressure and creates more space by spraying water!

24. Combined Gas Law P 1 V 1 T 2 = P 2 V 2 T 1 Shows the relations between variables and predicts results of adjustments made to system. Use for changing conditions! If one variable is constant, enter the same value twice or remove that variable from the equation.

25. STP Conditions Standard temperature is 273 K Standard pressure can be 1 atm 101.3 kPa 760 torr 760 mmHg

26. A 50. L sample of a gas at a pressure of 1.0 atm and a temperature of 25 o C is moved to an area where the pressure is 5.0 atm and the temperature is 30 o C. What is the new volume of the gas? P 1 V 1 T 2 = P 2 V 2 T 1 (1.0atm)(50.L)(30+273K) = (5.0atm)(X)(25+273) 15150 = 1490X 10. L V1V1 P1P1 T1T1 P2P2 T2T2

27. A 50.0 mL sample of a gas has a pressure of 2.00 atm when the temperature is 25 o C. What volume will the gas occupy at a pressure of 4.00 atm when a constant T? P 1 V 1 T 2 = P 2 V 2 T 1 (2.00atm)(50.0mL) = (4.00atm)(X) 100 = 4X 25.0 L V1V1 P1P1 T1T1 P2P2

28. A 5.0 mL sample at 20 o C has a pressure of 1.0 atm. What volume will the gas occupy when the temperature is raised to 60 o C at constant pressure? P 1 V 1 T 2 = P 2 V 2 T 1 (5.0mL)(60+273) = (X)(20+273) 1665 = 293X 5.7 mL V1V1 T1T1 P1P1 T2T2

29. A 20.0 mL sample of a gas has a pressure of 2.0 atm at a temperature of 20 o C. What will the temperature be when the pressure is raised to 4.0 atm at a constant volume. P 1 V 1 T 2 = P 2 V 2 T 1 (2.0atm)(X) = (4.0atm)(20+273) 2X = 1172 586K V1V1 P1P1 T1T1 P2P2