Unit 5: Gases – More Gas Laws: Charles’s Law and Boyle’s Law

1. Unit 5: Gases – More Gas Laws: Charles’s Law and Boyle’s Law 11.13 & 14Ms. Boon Chemistry

2. Objectives: • I can define Standard temperature and pressure. • I can state Charles’s Law & Boyle’s Law and use them to solve gas law problems. Catalyst • Standard temperature and pressure is 273K and 1 atm. • Is standard temperature cold or hot? Explain? • Where could you go to be at standard air pressure? Agenda • Catalyst • Balloon & Bottle • Charles’s Law • Boyle’s Law • Exit Slip HW: Complete mixed practice problems on worksheet.

3. Homework Review Pp. 445 #3, 9, 10, 24, 25 • 3. The fluidity of a gas is due to the fact that gas particles are widely separated and moving at high speeds. They move past each other easily. • The wide separation of gas particles also explains a gas’s compressibility. Because the particles are far apart, gases can be compressed or squished to fill a smaller volume. • The constant rapid, random motion of gas particles and the resulting collisions with each other and the walls of their container is what cause the pressure exerted by a gas.

4. Homework Review Pp. 445 #3, 9, 10, 24, 25 • 9. Two characteristics of an ideal gas are that it perfectly obeys the ideal gas law and conforms to the kinetic molecular theory. • 10. Diffusion is the process by which gas particles move from an area of high concentration to low concentration. The gas particles spread out until they are equally spread out.

5. Homework Review Pp. 445 #3, 9, 10, 24, 25 • 24. A gas’s pressure is directly proportional to temperature when volume is held constant. This is Gay-Lussac’s law. • 25. Gay-Lussac’s law can be explained using Kinetic Molecular Theory. Gas particles at higher temperature will have a higher average kinetic energy, which means that at constant volume they will collide with each other and with the walls of their container more often. This means that the particles exert more pressure because pressure is a measure of the force exerted per unit area.

6. Balloon & Bottle • The demonstration shows the relationship between ___________ and ____________. • As temperature increases, volume ___________________. As temperature decreases, volume ___________.

7. Balloon & Bottle • Summary of Procedure: (1) A small amount of water (~15 mL) is poured into an empty Erlenmeyer flask. (2) The flask is heated until steam comes out and the water boils for about 30 seconds. (3) Then the flask is removed from the heat and a balloon is attached over the mouth of the flask. Hypothesis: What do you think will happen to the balloon? Why?

8. Balloon & Bottle: Explanation • When we put the flask on the hot plate, the temperature of the gas inside the flask increases. The fast moving gas particles take up a large amount of volume. • When we put the balloon on the bottle, we fix the number of gas molecules in the bottle and balloon. • The gas temperature begins to decrease because we took the flask off the heat. • This causes a decrease in volume. • Describe what happened using the kinetic molecular theory of gases!

9. Charles’s Law: Temperature and Volume Relationships • Around 180o, Jacques Charles discovered that gas volume and absolute temperature are directly proportional at constant pressure. • For example, if the absolute temperature (temperature expressed in Kelvin) is doubled, the volume is doubled. If the volume is cut in half, the absolute temperature is also cut in half.

10. When gas pressure is held constant, the following equation expresses the volume and temperature relationship: • If any three of the variables in the above equation are known, then the unknown fourth variable can be calculated.

11. Example 1: V1 = 100 L, T1 = 100 K, V2 = ??, T2 = 200 K

12. Example 2: At 273K, the volume of a sample of nitrogen is 30 L. What will the temperature be if the volume increases to 300 L?

13. Example 3: At 500K, a 1000 mL sample is at standard pressure. If the pressure is held constant and the temperature decreases to 5K, what is the new volume in mL?

14. Boyle’s Law: Pressure and Volume Relationships • In 1662, English scientist Robert Boyle discovered that gas volume and pressure are inversely proportional at constant temperature. • For example, if the pressure is doubled, the volume is cut in half. If the volume is cut in half, the pressure is doubled.

15. When gas temperature is held constant, the following equation expresses the volume and pressure relationship: • If any three of the variables in the above equation are known, then the unknown fourth variable can be calculated. https://www.youtube.com/watch?v=DcnuQoEy6wA

16. Example 1: V1 = 100 L, P1 = 100 atm, V2 = ??, P2 = 20 atm

17. Example 2: A sample of gas occupies 523 mL at 1.00 atm. The pressure is increased to 1.97 atm, while the temperature remains the same. What is the new volume?

18. Example 3: A sample of gas occupies 100 L at 2.00 atm. The pressure is decreased to 760 mm Hg. What is the new volume?

19. If you see STP (standard temperature and pressure) you should immediately think: 0° C (or 273K) and 1 atm (or 760 torr or 760 mm Hg) • Standard Temperature and Pressure: Example: A balloon filled with helium has a volume of 22.4 L at standard temperature and pressure. If the temperature is held constant, what will the volume be at 2.0 atm?

20. Exit Slip 4c 11.13 & 14 • At constant pressure, as temperature increases, volume __________. Volume and temperature are _________ proportional. • At constant temperature, as pressure increases, volume __________. Volume and pressure are _________ proportional. • A sample of nitrogen has a volume of 275 mL at 273 K. The sample is heated and the volume becomes 550 mL. What is the new temperature in Kelvins? • A sample of gas occupies 1.55 L at 27.0° C and 1.00 atm pressure. What will the volume be if the pressure is increased to 50.0 atm, but the temperature is kept constant?