GasesChapter 11CHM 130

GCC

11.1 Properties of Gases1.Gases have no shape: they take the shape of

their container

2.Gases can expand & compress: V increases and atoms get farther apart, V decreases and atoms get closer together

3.Gases have low densities: air is about 0.001 g /mL

4.Gases mix completely with other gases: air is a mix of many gases like N2 (78%), O2 (21%), CO2, and noble gases

5.Gases exert pressure: they hit the sides of their container (exert force)

11.2 PressurePressure increases if

– Number of collisions increase (more hits)– Energy of collisions increase (harder hits)

There is no pressure in a vacuum

Atmospheric pressure– Force of air above us hitting us– What happens if you climb Mt. Everest?

As you climb, there is less air above you so pressure lessens, the air up high is less dense

1.00 atm = 760 torr =

760 mm Hg=14.7 psi

Barometer

The pressure of the air at sea level pushes the mercury liquid up 760 mm high.

P Conversions

A diver’s tank is at 4400 psi. Convert to torr, atm, and mmHg.

4400 psi ( 1 atm / 14.7 psi) = 3.0 x 102 atm

4400 psi( 760 torr / 14.7 psi) = 230,000 torr

230,000 torr = 230,000 mmHg

11.3 What affects Pressure?

1. If V increases, P ______

2. If T increases, P ______

3. If # gas atoms increases, P _____

Direct or Indirect Relationship?

1. P and V

2. P and T

3. P and # atoms

Decreases

Increases

Increases

Indirect

Direct

Direct

Gas Laws11.4 Boyle’s Law:

11.5 Charles’s Law:

11.6 Gay-Lussac’s Law:

P1V1 = P2V2

V1 = V2

T1 T2

P1 = P2

T1 T2

11.7 Combined Gas Law: P1V1 = P2V2

T1 T2

STP = standard temperature and pressure = 1 atm and 0°C

Videos if time

• Sulfur Hexafluoride gashttp://www.youtube.com/watch?v=u19QfJWI1oQ&feature=youtube_gdata_player

• How Density affects your voicehttp://www.youtube.com/watch?v=d-XbjFn3aqE&feature=youtube_gdata_player

• Boyle’s law and lungs http://www.youtube.com/watch?

v=NB1aCBId6qA • Boyle’s law and diving http://www.youtube.com/watch?

v=sRrniZ0anCE&feature=related

Gas Law Calculations

• T must be in Kelvin (oC + 273 = K)• V same units on both sides to cancel• P same units on both sides to cancel• Identify all variables as before (1) or

after the change (2)• If P, V, or T stays the same or is not

mentioned, it cancels out• Plug in and solve, keep track of units

and sig figs

A sample of krypton gas occupies 3.91 L at 105oC. Find the temperature in oC of the gas if the volume is changed to 6.05 L.

A sample of carbon dioxide gas occupies 2.25 L at 758 torr. Find the final volume if the pressure is decreased to 698 torr.

P1V1 = P2V2

V2 = P1V1 / P2

V2 = (758 torr)(2.25L) / (698 torr)

V2 = 2.44 L

V1/T1 = V2/T2

T2 = V2T1 / V1

T2 = (6.05 L)(378 K) / 3.91 L

T2 = 585 K and 585-273 = 312oC

A steel container filled with nitrous oxide at 15.0 atm is cooled from 25.5°C to –40.8°C. Calculate the final pressure.

A nitrogen gas sample occupies 50.5 mL at –82.8°C and 1250 torr. What is the volume at STP?

P1/T1 = P2/T2

P2 = P1T2 / T1

P2 = (15.0 atm)(232.2 K) / (298.5 K)

P2 = 11.7 atm

P1V1/T1 = P2V2/T2

V2 = P1V1T2 / T1P2

V2 =

V2 = 119 mL

torr)K)(760 (190.2

5mL)(273K torr)(50.1250

Dalton’s Law & Respiration (for fun)• Total P = sum of partial P• Ptot = P1 + P2 + P3 etc.• O2 is 21% of air by volume, so 21% of air P is due to O2 which

is about 160 torr.• When blood exposed to air in lungs, the oxygen diffuses into

the blood until the partial pressure in the liquid equals that of the gas in air

• Gases move from a region of higher partial pressure to lower partial pressure

• Partial pressure of O2 in pulmonary blood only about 40mmHg, compared to 104mmHg in alveoli. Diffusion occurs rapidly.

• Partial P defined http://www.youtube.com/watch?v=tTGehRESHmA&feature=related

• Diffusion http://www.youtube.com/watch?v=BatxnX5tXE0&feature=autoplay&list=PLB02A0A4A48238E7F&index

• CO2 transport http://www.youtube.com/watch?

v=x26TWL3VKMg&feature=mr_meh&list=PLB02A0A4A48238E7F&index=19&playnext=0

Self Test

• Page 320

• Try 1-7, 12-13, 15-16

• Answers in Appendix J