Gases
Chapter 11
CHM 130
GCC
11.1 Properties of Gases
1.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 Pressure
Pressure 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
Barometer
1.00 atm =
760 torr =
760 mm Hg=
14.7 psi
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?
Decreases
1. If V increases, P ______
2. If T increases, P ______
Increases
3. If # gas atoms increases, P _____
Increases
Direct or Indirect Relationship?
1. P and V
2. P and T
3. P and # atoms
Indirect
Direct
Direct
Gas Laws
11.4 Boyle’s Law: P1V1 = P2V2
11.5 Charles’s Law: V1 = V2
T1
T2
11.6 Gay-Lussac’s Law: 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 gas
http://www.youtube.com/watch?v=u19QfJWI1oQ&feature=youtube_gdata_player
• How Density affects your voice
http://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 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 = (758 torr)(2.25L) / (698 torr)
V2 = P1V1 / P2
V2 = 2.44 L
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.
V1/T1 = V2/T2
T2 = (6.05 L)(378 K) / 3.91 L
T2 = V2T1 / V1
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.
P1/T1 = P2/T2
P2 = (15.0 atm)(232.2 K) / (298.5 K)
P2 = P1T2 / T1
P2 = 11.7 atm
A nitrogen gas sample occupies 50.5 mL at –82.8°C
and 1250 torr. What is the volume at STP?
P1V1/T1 = P2V2/T2
V2 = P1V1T2 / T1P2




1250
torr)(50.
5mL)(273K
V2 = 


(190.2K)(760torr) 

V2 = 119 mL
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