Which of the choices shows the 3 phases of matter correctly ranked by amount of kinetic energy ?

1. Warmup (2 minutes) 2) Which of the choices shows the 3 phases of matter correctly ranked by density? a. liquid < gas < solid b. solid < liquid < gas c. solid > liquid > gas d. gas > solid > liquid • Which of the choices shows the 3 phases of matter correctly ranked by amount of kinetic energy? a. liquid < gas < solid b. solid < liquid < gas c. solid > liquid > gas d. gas > solid > liquid

2. Properties of Gases

3. IM Forces keep molecules “stuck together” Kinetic Energy:energy due to the motion of an object

4. K.E. and IMFs: 3 States of Matter Solids have: - molecules which are tightly packed; strong IM forces - low amount of kinetic energy; can only ‘vibrate’ Liquids have: - molecules which are tightly packed but IM forces stretched/broken - medium amount of kinetic energy; molecules “flow” Gases have: - no IM forces between molecules, which are free to move independently of one another - TONS of kinetic energy; molecules move wherever

5. The Kinetic Molecular Theory of Gases makes 5 assumptions about ideal gas behavior: 1. A gas is considered to be composed of tiny hard spheres 2. Molecules are far enough apart that we can ignore their volume. 3. Gas molecules have a lot of kinetic energy and are constantly in motion

6. 4. No energy is lost when particles collide with container walls or each other 5. There are NO forces of attraction or repulsion between gas particles because they move quickly in straight lines

7. 6 Physical Properties of Gases • Expansion • molecules expand in volume to fill a larger space. Compression • Volume can be decreased to fill a smaller space. Fluidity • Molecules flow past each other without getting stuck together. • Low Density • molecules have mass in a larger amount of volume Effusion • movement of molecules through a tiny opening. Start demo: volunteers with goggles

8. Diffusion: the tendency for a molecule to move from an area of high to low concentration Demo: Which gas will diffuse faster, NH3 or HCl? Describe the relationship between diffusion rate and identity of a gas. NH3(g) + HCl(g) NH4Cl(s)

9. RNH3 = √MMHCl RHCl = √MMNH3 RNH3 = √36.46 RHCl √17.04 RNH3 = 6.038 RHCl4.128 NH3 diffuses 1.463 times faster than HCl (some experimental error regarding conditions) Grahm’s Law: the effusion rate of a gas is inversely proportional to the square root of the gas density or molar mass • R(m/s) = 1/(√ molar mass) OR • R1= √MM2 • R2 √MM1

10. Grahm’s Law Demo Data Analysis Near which side is the NH4Cl ring? The hydrochloric acid (HCl) side Conclusion Which gas diffuses faster? Why? ammonia (NH3) Error Analysis What are some errors present in this demonstration? Q-tips in at the same time? Gases diffused through air, not a vacuum Concentration affects density. • HCl(g) + NH3(g)  NH4Cl(s) • Materials • clear straw • two Q-tips • concentrated NH3 • concentrated HCl • Procedure • Wet a Q-tip with each solution. • Place end of Q-tip at either end of the straw. • 3) Wait 5 minutes

11. A vial of uranium hexafluoride gas and a vial of hydrogen are sitting in a lab at standard temperature. Calculate and compare the effusion rates (in m/s) of the two gases. R H2 = 1/(√ molar mass) = 1/ √(2.02) = 0.704 m/sec R UF6 = 1/ √(352) = 0.0533 m/sec 0.704 m/sec = 0.0533 m/sec Hydrogen gas effuses 13.2 times faster than uranium hexaflouride

12. The effusion rate of Gas X was measured and found to be 24.0 ml/min. Under the same conditions, the rate of effusion of pure methane (CH4) gas is 47.8 ml/min. Which of these is most likely the identity of the gas? a) I2 b) SO2 c) C4H10 d) HCl Note: wouldn’t it be fun to merge this question with an empirical formulas question???????

13. Pressure is caused by collisions of the molecules with the sides of a container. The more often molecules of air strike a single spot, the more pressure is applied there! Temp: Temp: Low High Heat Gas Pressure: Pressure: Low High

14. How exactly do we use a barometer to measure atmospheric pressure? (*a manometer uses water) 1 atm Pressure 760 mm 1 atm = 760 mm Hg Column of Mercury Dish of Mercury

15. Units of Pressure • atm (atmospheres) • mm Hg (millimeters of Mercury) • kPa (kiloPascals) • 1 atm = 760 mm Hg = 760 torr = 14.7 psi = 101.3kPa • Silly Suzy and Bozo Joe are arm wrestling! Suzy exerts a pressure of 1890 mmHg. Joe exerts a pressure of 140 kPa. Who will probably win? • 1890 mmHg (101.3 kPa) = 252 kPa • (760 mmHg)

16. Kinetic Energy and Temperature • Temperature measures the average KE • Faster molecules, higher temperature. If you change temperature from 300 K to 600 K, what will happen to the KE of the sample? The kinetic energy doubles. Average KE of a sample is directly proportional to the temperature in Kelvin If you change temperature from 300ºC to 600ºC, what will happen to the KE? KE doesn’t double: 873 K is NOT twice 573 K At what temperature would molecular motion stop? At 0 K (or -273⁰C), the KE would equal 0 Joules

18. Temperature and air pressure can vary from one place to another on the Earth, and can also vary in the same place with time. Can you think of examples? It is necessary to define standard conditions for temperature and pressure: STPStandard Temperature (273 K) and Pressure (1.0 atm)