1112827252.pptx powerpoint presentation...

lesson

1. Gas Laws Charles, Boyle, Gay- Lussac, Combined and The Ideal Gas Law

2. PROPERTIES OF GAS 1. Gas particles come in the form of atoms or molecules. 2. Gases match the shape and volume of their containers. 3. The distances among gas particles are larger than the distances among particles of liquid and solid. 4. Gas particles are highly compressible. 5. Gas particles move in free, constant, and random motion. 6. Intermolecular forces among gas particles are weak and negligible. 7. Gases act upon changes in temperature. 8. Gas particles diffuse or spread out.

3. Kinetic-Molecular Theory The KINETIC MOLECULAR THEORY is based on the idea that particles of matter are always in motion. It says... Gases have no volume Gases are in constant, random motion. Gases d o not attract or repel each other. Gases have elastic collisions. The average kinetic energy of gas particles is directly related to their temperature.

4. Kinetic-Molecular Theory The KINETIC MOLECULAR THEORY is based on the idea that particles of matter are always in motion. It says... Gases have no volume Gases are in constant, random motion. Gases d o not attract or repel each other. Gases have elastic collisions. The average kinetic energy of gas particles is directly related to their temperature.

5. Kinetic-Molecular Theory The KINETIC MOLECULAR THEORY is based on the idea that particles of matter are always in motion. It says... Gases have no volume Gases are in constant, random motion. Gases d o not attract or repel each other. Gases have elastic collisions. The average kinetic energy of gas particles is directly related to their temperature.

6. Kinetic-Molecular Theory The KINETIC MOLECULAR THEORY is based on the idea that particles of matter are always in motion. It says... Gases have no volume Gases are in constant, random motion. Gases d o not attract or repel each other. Gases have elastic collisions. The average kinetic energy of gas particles is directly related to their temperature.

7. Kinetic-Molecular Theory The KINETIC MOLECULAR THEORY is based on the idea that particles of matter are always in motion. It says... Gases have no volume Gases are in constant, random motion. Gases d o not attract or repel each other. Gases have elastic collisions. The average kinetic energy of gas particles is directly related to their temperature.

8. Kinetic-Molecular Theory The KINETIC MOLECULAR THEORY is based on the idea that particles of matter are always in motion. It says... Gases have no volume Gases are in constant, random motion. Gases d o not attract or repel each other. Gases have elastic collisions. The average kinetic energy of gas particles is directly related to their temperature.

9. Variables That Effect Gases Moles (n) — the amount of gas. Volume (V) — the size of the container that holds the gas in liters (L). Te mp erat u re (T) — the speed or kinetic energy of the particles in kelvin ( o C +273) Pressure (P) — The outward push of gas particles on their container in atmospheres (atm), millimeters of mercury (mm Hg), kilopascals (kPa) or torr (torr). *Think of pressure as the number and strength of collisions between gas particles and their container.

10. FACTORS THAT A FFE CT THE BEHAVIOR OF GASES PRESSURE (P) - the dance movement T E MPERATUR E (T) - beat of the size of room AMOUNT (n) - /t of dancers

11. STP The behavior ol a gas depends on its temperatu r e and the pressure at which the gas is held. So far we have only dealt with gases at STP. Standard Temperature and Pressure. 273 kelvins and 1 atm.

12. UNIT HELP! Pressure Units 1 standard atmosphere (atm) 760 mm Hg (torr) = 29.2 inches Hg 101.3 kPa

13. UNIT HELP! Temp Units Celsius Kelvin = C + 273.15 Volume Units mL, L, cm3 n Units moles

14. The Gas Laws n Boyle's Law Charles's Law Gay- Lussac’s Law The Combined Gas Law The Ideal Gas Law

15. Boyle's Law The Pressure- Volume Relationship The pressure of a fixed mass of gas varies indirectly with the volume What remains constant? What changes? (As one goes up, the other goes down) P 1 V 1 2 2 If 3 of the variables are known, the fourth can be calculated.

16. W1• 1 L Ą 265 Ph — - 100 kPa P 2 100 kPa

17. Boyle's Law The gas in a 20.0mL container has a pressure of 2.77atm. When the gas is transferred to a 34.0mL container at the same temperature, what is the new pressure of the gas. 1 1 2 V 2 ' ' 2 J, 20.0mL(2.77o/m) 2 34.0mL P2 1.63orm P2

18. Boyle's Law So, does it make sense? If a set amount of gas is transferred into a larger container, would the pressure go up or down? Would there be more collisions, or fewer collisions with the container holding the gas? e More volume (space) means fewer collisions with the container, therefore pressure goes down. (From 2.77 atm to 1.63 atm)

19. Charles's Law Ti T2 The temperature- volume relationship The volume of a fixed mass of gas varies directly with the temperature. What remains constant? What changes? (As one goes up, the other goes up.) If 3 ol the variables are known, the fourth can be calculated.

20. Charles's Law 200 800 1000 400 600 Tempe<au<elK)

21. 300 K 100 kPa 600 200 kPa

22. Charles Law ViT2 7i What will be the volume of a gas sample at 355K if its volume at 273K is 8.57L? 8.57L(355ke/vín) 273kefvin 2

23. Charles's Law Does it make sense? e If the temperature of a given quantity of gas is increased, what will happen to the volume it occupies? (In an elastic container?) Gas particles moving faster would have more collisions with the container and exert more force to enlarge the volume of the elastic container. e In this case, from 8.57L to 11.1 L.

24. P1 P2 Al' 2 Gay- Lussac’s Law n The Temperature- Pressure Relationship The pressure of a fixed mass of gas varies directly with the temperature at a constant volume. What is constant? What is changing? (If one goes up, the other goes up.) ■ |f you know 3 of the variables, you can calculate the 4 h .

25. Gay- Lussac’s Law The gas left in a used aerosol can is at a pressure of 2.03atm at 25 o C. If this can is thrown onto a fire, what is the pressure of the gas when its temperature reaches 928 o C? P1 P2 Ti T2 P1T2 P2 2 J, 2.03<rm(12017€) 298/? P2 8.18u›m

26. Gay- Lussac’s Law Does it make sense? If the temperature of a fixed amount of gas goes up, the particles will have more collisions. More collisions means the pressure will increase. In this case, when the temp went up the pressure increased from 2.03atm to 8.18atm.

27. ressure - Temperamre - Volume Relationship Boyle's Charles P a V a T Gay- Lussac’s P ’^ T

28. The Combined Gas Law Expresses the relationship between pressure, temperature, and volume of a fixed amount of gas. What is constant? P1 1 P2 2 T T2 5 of the variables must be known to calculate the 6 h .

29. The Combined Gas Law The volume of a gas- filled balloon is 30.OL at 40 O C and 1.75atm of pressure. What volume will the balloon have at standard temperature and pressure? 2 2 — P›VI P2)Z*2 Ti T2 ViPiT2 P2Ti 30.0L(1.75nrm)(2737€) 1.00nrm(313/?) 2 — 45.8L

30. The Combined Gas Law Does it make sense? You have a fixed volume of gas. The temperature decreases which would cause fewer collisions and the pressure decreases which causes fewer collisions as well. What can you do to volume to make the pressure decrease??? Increase it. More space means fewer collisions.

31. The Ideal Gas Law Describes the physical behavior of an ideal gas in terms of the pressure, volume, temperature and the number of moles of gas. Ideal — a gas as it is described by the kinetic- molecular theory postulates. All gases are REAL gases... which behave like ideal gases only under most ordinary conditions. W

32. The Ideal Gas Law Only at very low temperatures and very high pressures do real gases show significant non- ideal behavior. We will assume that gases are close to ideal and that the ideal gas equation applies.

33. Ideal Gas Equation PV=nRT P- pressure V- volume n- number of moles of gas R- ideal gas constant (universal gas constant) 0.0821 atm•L/moI•K 8.314 kPa • L/moI•K 62.396 torr•L/moI•K 62.4 mmHg•L/moI•K T- temperature

34. Ideal Gas Equation What is the volume occupied by 9.45g of C 2 H 2 ?t t STP? PY nRT ft »T First, calculate amount of gas in moles. n 9.45gC2H2 MOJ 2H 2 26.03788gC2V2 n 0.3629328mfi/ 2H2

35. Ideal Gas Law nRT 0.3629328mo/(0.0821oriti • L/ ino/ • 7ć)273k 1.00nrm Y 8.1345217L V 8.13L

36. Ideal Gas Law How many moles of a gas at 100 o C does it take to fill a 1.00L flask to a pressure of 1.5atm? PV nRT qp 1.5orm(1.OOL) 0.0821orm • L/ mr/ • /P(373k) n 0.049mo/

37. Lifting Power of Gases For a gas to be used to inflate lighter- than- air craft like balloons and blimps, the gas must have a density lower than air. The lower the density, the greater the lifting power.

38. Lifting Power of Gases e The density of a gas depends on its pressure, temperature and molar mass. Each of these variables is part of the ideal gas law. Therefore, we should be able to adjust each of these variables to give low density.

39. Lifting Power of Gases e However, if the pressure of the gas within a balloon or blimp were significantly less than the atmospheric pressure, the balloon or blimp would be crushed. e Therefore, only two factors can be manipulated to lower the density of a gas: molar mass and temperature

40. Molar Mass Gases with low density can be corrosive, combustible, flammable or chemically active in some way. These gases would make poor choices to fill blimps and balloons. Helium, due to its small molar mass and chemical inactivity is the primary choice for balloons and blimps.

41. Temperature Helium is relatively rare and very expensive, so hot air is often preferable. As the temperature of a gas is increased, the particles increase the number of collisions and increase the pressure inside the balloon. The volume of the balloon increases and becomes less dense and rises. Hot air does not have the same lifting power as helium, but it is much cheaper.

42. Gas Effusion The movement of atoms or molecules through a hole so tiny that they do not stream through but instead pass through one particle at a time. Explains why helium balloons deflate slowly over a period of a few hours. The lower the mass of the gas, the greater the speed of its particles. Hydrogen effuses faster than helium. Helium effuses faster than oxygen.