Gay-Lussac

1
Gay-Lussacs Law P and T

• the pressure exerted by a gas is directly related
  to the Kelvin temperature.
• V and n are constant.
• P1 P2
• T1 T2

2
Calculation with Gay-Lussacs Law

• A gas has a pressure of 2.0 atm at 18C. What
• is the new pressure when the temperature is
• 62C? (V and n constant)
• 1. Set up a data table
• Conditions 1 Conditions 2
• P1 2.0 atm P2
• T1 18C 273 T2 62C 273
• 291 K 335 K

?
3
Calculation with Gay-Lussacs Law (continued)

• 2. Solve Gay-Lussacs Law for P2
• P1 P2
• T1 T2
• P2 P1 x T2
• T1
• P2 2.0 atm x 335 K 2.3 atm
• 291 K
• Temperature ratio
• increases pressure

4
Try it

• A gas has a pressure of 645 torr at 128C. What
  is the
• temperature in Celsius if the pressure increases
  to
• 1.50 atm (n and V remain constant)?
• 1. Set up a data table
• Conditions 1 Conditions 2
• P1 645 torr P2 1.50 atm x 760 torr
  1140 torr
• 1 atm
• T1 128C 273 T2 ?K ? K
  273 ?C
• 401 K

5
Solution

• 2. Solve Gay-Lussacs Law for T2
• P1 P2
• T1 T2
• T2 T1 x P2
• P1
• T2 401 K x 1140 torr 709 K - 273
  436C
• 645 torr
  Pressure ratio
• increases temperature

6
Avogadro's Law Volume and Moles

• the volume of a gas is directly related to the
  number of moles (n) of gas.
• T and P are constant.
• V1 V2
• n1 n2

7
Learning Check

• If 0.75 mole helium gas occupies a volume of 1.5
  L, what volume will 1.2 moles helium occupy at
  the same temperature and pressure?

8
Solution

• STEP 1 Conditions 1 Conditions 2
• V1 1.5 L V2 ???
• n1 0.75 mole He n2 1.2 moles He
• STEP 2 Solve for unknown V2
• V2 V1 x n2
• n1
• STEP 3 Substitute values and solve for V2.
• V2 1.5 L x 1.2 moles He 2.4 L
• 0.75 mole He

9
STP and Molar Volume
STP standard temperature (273 K) and pressure
(1 atm)
At STP 1 mol of a gas (any gas) has a volume of
22.4 L 22.4 L 1 mole
molar volume
Can be used as a conversion factor a) What is
the volume of 2.50 moles of N2 at STP? b) What
is the volume in liters of 6.40 g of O2 at STP?
10
Partial Pressure Daltons Law

• Many gases are mixtures of gases, e.g. air.
• The partial pressure of a gas
• is the pressure of each gas in a mixture.
• is the pressure that gas would exert if it were
  by itself in the container.

11
Daltons Law of Partial Pressures

• Daltons Law of Partial Pressures indicates that
• pressure depends on the total number of gas
  particles, not on the types of particles.
• the total pressure exerted by gases in a mixture
  is the sum of the partial pressures of those
  gases.
• PT P1 P2 P3 .....
• So if total pressure (PT) is known and all but
  one partial pressure..can determine partial
  pressure of that one.

12
Learning Check

• A scuba tank contains O2 with a pressure of
  0.450 atm and He at 855 mm Hg. What is the
  total pressure in mm Hg in the tank?

13
Solution

• 1. Convert the pressure in atm to mm Hg
• 0.450 atm x 760 mm Hg 342 mm Hg P(O2)
  1 atm
• 2. Calculate the sum of the partial pressures.
• Ptotal P(O2) P(He)
• Ptotal 342 mm Hg 855 mm Hg
• 1197 mm Hg

14
Learning Check

• For a deep dive, a scuba diver uses a mixture of
  helium and oxygen with a total pressure of 8.00
  atm. If the oxygen has a partial pressure of
  1280 mm Hg, what is the partial pressure of the
  helium?

PTotal 8.00 atm x 760 mm Hg 6080 mm
Hg 1 atm PTotal PO PHe
2 PHe
PTotal - PO2 PHe 6080 mm Hg -
1280 mm Hg 4800 mm Hg
15
Gases We Breathe

• The air we breathe
• is a gas mixture.
• contains mostly N2 and O2 and small amounts of
  other gases.

16
Learning Check

• A.If the atmospheric pressure today is 745 mm Hg,
  what is the partial pressure (mm Hg) of O2 in the
  air?
• 1) 35.6 2) 156 3) 760
• B. At an atmospheric pressure of 714, what is the
  partial pressure (mm Hg) N2 in the air?
• 1) 557 2) 9.14 3) 0.109

Hint air is 21 oxygen
17
Blood Gases
Lungs
18
Blood Gases

• In the lungs/blood/body
• O2 flows (combined with hemoglobin) into the
  tissues because the partial pressure of O2 is
  higher in arterial blood, and lower in the
  tissues.
• CO2 flows out of the tissues because the partial
  pressure of CO2 is higher in the tissues, and
  lower in the blood.
• Partial Pressures (mmHg) in Blood and Tissue
• Oxygenated Deoxygenated
• (arterial) (venous)
• Gas Blood Blood Tissues
• O2 100 40
  30 or less
• CO2 40
  46 50 or greater