CH110 Chpt 7 Gases

CH110 Chapter 8: Gases

Kinetic Molecular Theory

Pressure

Gas Laws

CH110 Chpt 7 Gases

Solid

Liquid

Vapor

Slow moving, dense,Fixed shape

Moderate movement,Dense,Takes shape of container

Fast moving, Low density,Expands to fill container

Density Shape Compressibility

Small compressibility,

Very small heat expansion

Large compressibility,

Expands w/ heat

Smallcompressibility,

Small heat expansion

CH110 Chpt 7 Gases

1. All gases are made up of tiny particles moving in • straight lines • in all directions • at various speeds.

Kinetic molecular theory of Gases

Model to explain behavior of gases

Vapor

CH110 Chpt 7 Gases

3. V of a gas = V of container

V of a gas is mostly empty space.

2. Particles far apart have no effect on each other. (Don’t attract or repel)

Kinetic molecular theory

CH110 Chpt 7 Gases

Kinetic molecular theory

4. The ave KE as the T

• The average KE is the same for all gases at the same T.

TKE

(K.E. a T)

CH110 Chpt 7 Gases

5. Gas molecules exert pressure as they collide with container walls

The > the # of collisions (per unit time), the > the pressure

Kinetic molecular theory

CH110 Chpt 7 Gases

6. E is conservedwhen colliding with each other or container walls.

For an Ideal Gas Collisions are perfectly elastic & no E is gained or lost. (Like billiard balls exchanging E.)

CH110 Chpt 7 Gases

6. E is conservedwhen colliding with each other or container walls.

For an Ideal Gas Collisions are perfectly elastic & no E is gained or lost. (Like billiard balls exchanging E.)

CH110 Chpt 7 Gases

Pressure= Force per unit of Area. Force

AreaP = Force

Area

In the atmosphere, molecules of air (N2, O2, Ar, H2O, etc..) are constantly bouncing

off us.

CH110 Chpt 7 Gases

We live at the bottom of an ocean of air

Atmospheric Pressure

Atmosphere:A sea of colorless, odorless gases surrounding the earth

CH110 Chpt 7 Gases

PressureAt higher elevations, there is less air so the P is less.

CH110 Chpt 7 Gases

Boiling Point = Temp where molecules

overcome atmospheric Pressure

Sea Level

760 torrDenver (5280’)

630 torrMt. Evans,CO(14,000’)

Mt. Everest(20,000’)

467 torr

270 torr H2O

= 100 oC

= 95 oC

= 87 oC

= 73 oC

CH110 Chpt 7 Gases

Measuring PressureAttempts to

pump water out of flooded

mines often failed because

H2O can’t be

lifted more than 34 feet.

CH110 Chpt 7 Gases

Measuring PressureTorricelli believed reason was that P of atmosphere could not hold anything heavier than a 34’ column of water.

CH110 Chpt 7 Gases

Like drinking from a straw.

What causes the liquid to move up the straw to your mouth ?

Atmospheric Pressure

CH110 Chpt 7 Gases

34’ columnof water

1 Atm

The atmosphere

would support a column of

H2O> 34 feet high.

Measuring Pressure

CH110 Chpt 7 Gases

Torricelli BarometerPressure of the atmosphere supports acolumn of Hg 760 mm high.

1 atm

1 atm =760 mm Hg760 torr29.92 in Hg14.7 lb/in2

101,325 Pa

vacuum

Mercury used because it’s so dense.

CH110 Chpt 7 Gases

Blood pressure (systolic over diastolic):most often in mm Hg. (ex. 120/80)

Meteorologists refer to pressure systems in mm or inches of Hg. ex. 30.01 in

CH110 Chpt 7 Gases

STPStandard Temperature & Pressure

1 atm

1 atm =760 mm Hg760 torr29.92 in Hg14.7 lb/in2

101,325 Pa

0oC

273K

CH110 Chpt 7 Gases

Gas lawsLaws that show relationships between volume and properties of gasesBoyle’s LawCharles’ LawGay-Lussac’s Law

Avogadro’s LawDalton’s Law

CombinedGas Law

CH110 Chpt 7 Gases

V is inversely proportional to P when T is constant.

If P goes down V goes up

P

V

P V

P

V

Boyle’s law: V vs P

CH110 Chpt 7 Gases

P1 = 1 Atm

V1 = 1 L

P1V1 = P2V2 V2 =

P1V1 = V2

P2

1atm (1L) =

0.5 atm2 L

Boyle’s law: V vs P

2 L

P2 = 0.5 Atm

CH110 Chpt 7 Gases

1 L

Boyle’s law: V vs P2 L

Drive to top of mountain - ears start popping.

Breathing at high altitudes is more difficult because the pressure of O2 is less.

CH110 Chpt 7 Gases

It all “Boyle’s” down to Breathing in and out.

Boyle’s law

CH110 Chpt 7 Gases

Charles’s law: V vs TThe volume of a gas is directly proportional to the absolute temperature (K).

T V

P

If T goes up V goes up

CH110 Chpt 7 Gases

V1 = 125 mL

T1 = 273 K

Charles’s law: V vs T V1 = V2

T1 T2

V1 = V2

T1 T2

V2 =

T2 = 546 K

250 mL

(546K)125 mL = 273 K

T2V1 = V2

T1

CH110 Chpt 7 Gases

Gay-Lussac’s Law (PT)Pressure of a gas is directly proportional to

Absolute Temp (K) when Volume is constant

P1 = P2

T1 T2

P1 = P2

T1 T2

P T

V

If P goes up T goes up

CH110 Chpt 7 Gases

Boyle’s

Gay-Lussac’s

Charles’

PT

VV

T VP

TP

VGas LawsP1V1 = P2V2

V1 = V2

T1 T2

P1 = P2

T1 T2

CH110 Chpt 7 Gases

Boyle’s

Gay-Lussac’s

Charles’

CombinedGas Law

PT

VV

T VP

TP

VGas Laws

P1V1

T1

= P2V2

T2

CH110 Chpt 7 Gases

A 10 m3 balloon contains helium on the ground where the temperature is 27ºC and the pressure is 740 torr. Find the volume at an altitude of 5300 m if pressure is 370 mm Hg and temperature is -33 ºC.

P1 = 740 mm

T1 = 27 + 273 = 300 K

V1 = 10 m3

P2 = 370 mm

T2 = -33 + 273 = 240 K

V2 = ?

= 16 m3V2 = (240 K)(740 mm)(10 m3 )

(370 mm) (300 K)

P1V1

T1

= P2V2

T2

T2P1V1

P2 T1

= V2

Combined Gas Law

CH110 Chpt 7 Gases

Avogadro’s lawThe volume of a gas is directly

proportional to the number of molecules

V1 = V2

n1 n2

V1 = V2

n1 n2

More moles of a gas, takes up more space.

CH110 Chpt 7 Gases

At Standard Temperature & Pressure (STP)

V of 1 mole of gas = 22.4 liters

Equal volumes of gas (at same T and P)

contain equal numbers of molecules.

Avogadro’s law

At T = 273 K (0ºC) P = 1 atm (760 mm)

1 mol He

4 g He

22.4 L

1 mol He

4 g He

22.4 L

1 mol N2

28 g N2

22.4 L

1 mol N2

28 g N2

22.4 L

1 mol CO2

44 g CO2

22.4 L

1 mol CO2

44 g CO2

22.4 L

CH110 Chpt 7 Gases

Standard conditions (STP)When 2.00 mol of liquid H2O is vaporized,

how may liters of gas will there be?

2 mole H2O

1

22.4 liters

1 mole H2O= 44.8 L

22.4 liters

1 mole H2O1 mole H2O

22.4 liters

CH110 Chpt 7 Gases

Dalton’s law of Partial Pressures

The total pressure of a gas mix = sum of the partial pressures of each gas.

Pair = PN2 + PO2 + PAr + PCO2 + PH2O

PT = P1 + P2 + P3 + .....

Each gas acts independently of the others.

Example: Air

CH110 Chpt 7 Gases

Pair = PN2 + PO2 + PCO2 + PH2O = 760 mm

Dalton’s law of Partial Pressures

Typical values for Atmospheric air at 0 ºC (excluding argon):

(594.0mm)+(160mm) +(5.7mm)=+(0.3mm) 760mm

As T of air increases, more H2O enters mix.

example: at 20 ºC, the PH2O = 18 mm Ptotal (760 mm) can’t change, so other

gases get diluted to make room for the water.

CH110 Chpt 7 Gases

Air moving over warm water

has more water in it.

Low pressure

is often associated with this air.

Typhoons and hurricanes

are associated with very warm, moist air.

Pair = PN2 + PO2 + PCO2 + PH2O = 760 mm

CH110 Chpt 7 Gases

Blood Gases

PCO2 ~ 40 mm Hg

Normal PO2 in the air =160 mm.

If drops

< 100 mm,

can’t diffuse into the blood.

Arterial Blood Gases (ABGs)

PBG = PO2 + PCO2

PO2 ~ 100 mm Hg

PCO2 ~ 46 mm Hg

Venous Blood Gases (VBGs)

PO2 ~ 40 mm Hg

CH110 Chpt 7 Gases

We only use about 25% of the Oxygen we inhale.

The rest is exhaled along with the Nitrogen and some carbon dioxide.

THIS IS WHY CPR WORKS !!!

CH110 Chpt 7 Gases

Bernoulli's Principle

Faster moving gases exert less pressure than slow moving gases.

Fast moving Gases Low P

Slow moving Gases

High P

CH110 Chpt 7 Gases

Bernoulli's PrincipleSlow moving

Gases

Fast moving Gases

High P

Low P