1. Unit 5 - Gases Objective :
What are the fundamental properties of gases?
What laws best describe their behavior?
What theory explains these properties and laws?

2. The amount of air we breath
Everyday we move about 8500 L of air in to and out of your lungs.
The total mass of this air is 11kg (25lb)
How we can measure this air?
The answer is pressure

3. pressure
It’s the force exerted per unit area by gas molecules as they strike the surface around them
The higher the concentration of the gas molecules, the greater will be the pressure.

4. Formula: Pressure (P = force/area) Or P=F/A
“Molecular Push”
Formula: Pressure (P = force/area)
Or P=F/A
SI Unit: Newtons per square meter (N/m2)
Pascal (N/m2), kilopascal (kPa)
Pressure is measured using a barometer

5. Other units: mm Hg, atm, torr, bar, psi(pounds per square inch)
Pressure
Other units: mm Hg, atm, torr, bar, psi(pounds per square inch)
1 atm = kPa
1 atm = 760 mm Hg
1 mm Hg = 1 torr
1 atm = bar
1 atm= psi

6. Pressure Conversions
1) Convert 789 mm Hg to atm
2) A Canadian weather report gives the atmospheric pressure as kPa. What is the pressure in Torr?
3) What is the pressure in a rectangular container if the particles exert a force of 120 N? The container is 0.4 m long and m wide.

7. Measures atmosphere pressure in mmHg B. Manometer Types: Open & Closed
Pressure Devices
A. Barometer
Measures atmosphere pressure in mmHg
B. Manometer
Types: Open & Closed
Mercury is used because of its density ( = 13.6 g/cm3)

8. manometer

9. Boyle’s Law
For a given amount of gas at constant temperature, the volume of the gas varies inversely with its pressure
Mathematically P1V1=P2V2

10. Pressure – Volume Relationship

11. Video – Boyle’s law
processes/gas-phase/v/boyles-law

13. Example
1) A sample of helium occupies 535 mL at 988 Torr and 25˚C. If the sample is transferred to a 1.05 L flask at 25˚C, what will be the gas pressure in the flask?
Answer= 503 Torr

14. Example
2) A sample of air occupies 73.3 mL at 98.7 kPa and 0˚C. What volume will the air occupy at atm and 0˚C?
Answer: mL

15. Warm -Up
Why the second floor of the house is usually warmer than the first floor?
Answer is Charles's Law

16. Volume is proportional to temperature You must use Kelvin K= 273 + ˚C
Charles’s Law
Jacques Charles found that temperature and volume were directly related which means that if the volume goes up so does the temperature.
Volume is proportional to temperature
You must use Kelvin
K= ˚C
If you double the temperature you double the volume

18. Charles’s Law Problem
A sample of hydrogen occupies 692 L at 602°C. If the pressure is held constant, what volume will the gas occupy after cooling to 23°C?

19. Example
A balloon at indoors, where the temperature is 27˚C, has a volume of 2.00 L. What will its volume be outdoors, where the temperature is -23˚C?
Answer: 1.67 L

20. Review Problem
If the gas present in 4.65 L at STP is changed to a temperature of 15˚C and a pressure of 756 Torr, what will be the new volume?

21. Combines all three variables (pressure, volume, temperature)
Combined Gas Law
Combines all three variables (pressure, volume, temperature)
Temperature must still be in Kelvin

22. Example
A cylinder of gas is kept at a constant volume, as the temperature increases from ˚C to ˚C. If the initial pressure is atm, what is the final pressure in mmHg?
Answer: 1.55 X 103 mmHg

23. Example of Combined Gas Law
A gas occupies of a volume of 459 mL at 23ºC and 234 torr. What is the gas’s new volume if the temperature increases to 45ºC and the pressure doubles?

24. Example # 2
Aerosol containers often carry the warning that they should not be heated. Suppose such a container were filled with a gas at 2.5 atm and 22 ˚C, and suppose that the container may rupture if the pressure exceeds 8.0 atm. At what temperature is that rupture likely to occur?

25. Example # 3
A 350 mL sample of helium gas is collected at 22.0 oC and 99.3 kPa.  What volume would this gas occupy at STP?

26. STP
Standard Temperature and Pressure
Standard Temperature
273 K or 0˚C
Standard Pressure
1 atm or kPa

27. Example
A gas occupies of a volume of 634 mL at 30ºC and 335 kPa. What is the gas’s new volume if the temperature increases to 45ºC and the pressure goes to 800 kPa?

28. Avogadro's Law
What happens when the amount of gas changes?
As amount of gas increases, volume increases
V α n (at constant T and P)

30. Consider the inflation of a balloon

31. Problem
A chemical reaction occurring in a cylinder equipped with a movable piston produces mole of a gaseous product. If the cylinder contained mol of gas before the reaction and had an initial volume of 2.18L, what was its volume after the reaction? (Assume constant pressure and temperature and that the initial amount of gas completely reacts)

32. Warm up
A 56.0 mL sample of neon gas is at the same pressure as the prevailing barometric pressure. If the pressure of the gas in increased to Torr above the barometric pressure while the temperature is held constant, the volume is observed to change to 49.4 mL. What is the prevailing barometric pressure?
Answer= 748 Torr

33. Example
If all of the Helium is used to fill 1.5 L red balloons at 0.99 atm and 32 ˚C, how many balloons will you end up with?
This question corresponds to the question before.
Answer: V= 149L which equals 99 balloons

34. Ideal Gas Equation
Combining Boyle’s law, Charles's law and Avogadro’s law

35. Ideal Gas Law

36. P = pressure (atm)
V= Volume (L)
n= number of moles
R= L*atm/ K* mol
T= temperature (K)

37. Example
What is the pressure in atmospheres exerted by a mole sample of nitrogen gas in a 10.0 L container at 298 K?
Ans) atm

38. A 8. 5 L tank contains Helium gas at 16. 9 atm and 25˚ C
A 8.5 L tank contains Helium gas at 16.9 atm and 25˚ C. How many moles of He are available for making balloons?
If all of the Helium is used to fill 1.5 L red balloons at 0.99 atm and 32 ˚C, how many balloons will you end up with?
Answer: 5.9 mole He

39. Example
An unknown gas is collected in an mL vessel at 1.02 atm and 23 ˚ C. The evacuated vessel has a mass of g, and the vessel and gas have a combined mass of g. Find the molar mass of the gas
Answer: mol

40. Example
If 12.0 g O2 are required to inflate a 500 cm3 tire at 30°C, what pressure is present inside the tire? Assume the gas behaves ideally.

41. How many moles of N2 gas are in 0.38 L at 0ºC and 380 mm Hg?
Additional Problems
How many moles of N2 gas are in 0.38 L at 0ºC and 380 mm Hg?
What volume would 25.0 grams Argon occupy at 90°C and 735 torr?

42. Additional Problems
An electronic vacuum tube was sealed off during manufacture at a pressure of 1.8 x 10-5 torr at 27°C. Its volume is 100 cm3. Compute the number of gas molecules remaining in the tube.