Chapter 13 - GASESChapter 13 - GASES

Properties of gasesProperties of gases1.1. are compressibleare compressible

2.2. occupy all available volumeoccupy all available volume

3.3. one mole of gas at 0one mole of gas at 0ooC and 1 atm pressure C and 1 atm pressure occupies 22.4 litersoccupies 22.4 liters

4.4. gases have massgases have mass

5.5. can move (diffuse) through each othercan move (diffuse) through each other

6.6. gases exert pressuregases exert pressure

7.7. A gases pressure depends on temperatureA gases pressure depends on temperature

The properties of gases are The properties of gases are explained by the explained by the

Kinetic-Molecular Theory of GasKinetic-Molecular Theory of GasGases are composed of small particles Gases are composed of small particles that have mass.that have mass.

The particles are far apart (compared to The particles are far apart (compared to the volume of the particles). the volume of the particles).

They are in rapid motion and have They are in rapid motion and have perfectly elastic collisions perfectly elastic collisions

The collisions of gas molecules The collisions of gas molecules against the sides of a container against the sides of a container create pressure.create pressure.

The kinetic energy of a gas The kinetic energy of a gas molecule is given by the equation molecule is given by the equation KE = 1/2mvKE = 1/2mv22

Temperature is a measure of the Temperature is a measure of the average KE of gas molecules.average KE of gas molecules.

Lighter gas molecules, such as HLighter gas molecules, such as H22

move faster than heavier gas move faster than heavier gas molecules (Omolecules (O22) if they are at the ) if they are at the

same temperature.same temperature.

Measuring Gas - page 424Measuring Gas - page 424

The four variables needed to completely The four variables needed to completely describe a sample of gas are the amount describe a sample of gas are the amount of gas (moles), volume, temperature and of gas (moles), volume, temperature and pressure. pressure.

All types of gas behave the same so we All types of gas behave the same so we do not need to know what type of molecule do not need to know what type of molecule the gas is. the gas is.

Atmospheric pressure - the weight Atmospheric pressure - the weight of the atmosphere pushing on us. of the atmosphere pushing on us. 1 atm = 14.7 lb/in1 atm = 14.7 lb/in22 = 101,325 N/m = 101,325 N/m22 (Pa) (Pa) = 760 mm Hg= 760 mm Hg

760 mm Hg corresponds to the weight per 760 mm Hg corresponds to the weight per square inch that atmospheric pressure can square inch that atmospheric pressure can support support

If mercury is 13.6 times more If mercury is 13.6 times more dense than water, what is the dense than water, what is the

maximum water height that the maximum water height that the atmosphere can support?atmosphere can support?

A well any deeper than this must use A well any deeper than this must use a submersible pump. a submersible pump.

Start assignment (practice problems Start assignment (practice problems 1 & 2 page 427)1 & 2 page 427)

Enclosed gasesEnclosed gases

Absolute pressure - the true pressure of a Absolute pressure - the true pressure of a gas (barometric pressure is an example)gas (barometric pressure is an example)

Gage pressure - the difference in pressure Gage pressure - the difference in pressure between the trapped gas and the between the trapped gas and the atmosphere (tire pressure is an example).atmosphere (tire pressure is an example).

Manometer Manometer

A manometer can give the A manometer can give the true pressure of a gas by true pressure of a gas by adding or subtracting the adding or subtracting the height of the Hg column from height of the Hg column from the atmospheric pressure.the atmospheric pressure.

Draw a diagram and solve Draw a diagram and solve practice problems 3 and 4 on practice problems 3 and 4 on page 429.page 429.

Gas LawsGas Laws

One mole of gas = 22.4 liters at STP One mole of gas = 22.4 liters at STP (The standard temperature and (The standard temperature and pressure for gases is 0pressure for gases is 0ooC and 1 atm.)C and 1 atm.)

Boyle’s Law Boyle’s Law (pressure - volume relationship)(pressure - volume relationship)If we have a given quantity of gas If we have a given quantity of gas (moles) and the temperature is kept (moles) and the temperature is kept constant while the pressure and volume constant while the pressure and volume are changed, PV = constant (k).are changed, PV = constant (k).

PP11VV11 = P = P22VV22

The pressure times volume before the The pressure times volume before the change is equal to the pressure times change is equal to the pressure times volume after the change.volume after the change.

Do sample problem 3 page 433Do sample problem 3 page 433

Assignment continued (practice Assignment continued (practice problems 5,6 page 434)problems 5,6 page 434)

Charles’s Law (temperature - Charles’s Law (temperature - volume relationship)volume relationship)

If the pressure is kept constant, the If the pressure is kept constant, the temperature and volume are directly temperature and volume are directly proportional. As temperature increases, proportional. As temperature increases, the volume also increases.the volume also increases.

Experimental volume -temperature data Experimental volume -temperature data can be graphed and the line can be graphed and the line extended extended (extrapolated) to zero volume. (extrapolated) to zero volume.

VV11TT22 = V = V22TT11

Charles’s LawCharles’s Law

Absolute temperature scale Absolute temperature scale

There are no negative temperaturesThere are no negative temperatures

Absolute zero is the coldest possible Absolute zero is the coldest possible temptemp

(Kelvin scale, K) - nature’s (Kelvin scale, K) - nature’s temperature scaletemperature scale

K = K = ooC + 273.15C + 273.15

As the temperature of a gas is As the temperature of a gas is changed, the volume of gas will be changed, the volume of gas will be changed by a ratio of the initial and changed by a ratio of the initial and final temperature in final temperature in ooK.K.

Example problem: What will be the Example problem: What will be the new volume if 2 L of gas is heated new volume if 2 L of gas is heated from 100from 100ooC to 300C to 300ooC?C?

VV11TT22 = V = V22TT11

Show how to solve sample problem Show how to solve sample problem 4 on page 438.4 on page 438.

Assignment continued - page 438 Assignment continued - page 438 practice problems 7,8practice problems 7,8

Avogadro’s LawAvogadro’s Law

Equal volumes of gases at the same Equal volumes of gases at the same pressure and temperature will have pressure and temperature will have equal number of gas particles.equal number of gas particles.

Three moles of gas will occupy three Three moles of gas will occupy three times the volume as one mole of gas. times the volume as one mole of gas.

Dalton’s Law of Partial PressuresDalton’s Law of Partial Pressures

The sum of the partial pressures of all The sum of the partial pressures of all the components in a gas mixture is the components in a gas mixture is equal to the total pressure of the gas equal to the total pressure of the gas mixture.mixture.

PPTT = pa + pb + pc + pd + - - - - - = pa + pb + pc + pd + - - - - -

Problem assignment continued (page Problem assignment continued (page 440 practice p. 9 & 10440 practice p. 9 & 10

THE IDEAL GAS LAWTHE IDEAL GAS LAW

PV = nRTPV = nRT

R = 8.314 J/(mol K)R = 8.314 J/(mol K)

R = .0821 (atm L)/(mole K)R = .0821 (atm L)/(mole K)

R = 8.314 (Pa mR = 8.314 (Pa m33)/(mol K))/(mol K)

Use the R that has the correct units Use the R that has the correct units for the problemfor the problem

Problem assignment continued - Problem assignment continued - page 443 practice 11, 12page 443 practice 11, 12

Real gases Real gases

Real gases can deviate from the Real gases can deviate from the ideal gas equation at very high ideal gas equation at very high pressure and at very low pressure and at very low temperatures. This is because of temperatures. This is because of the slight attractive forces the slight attractive forces between real gases. between real gases.

““Free-style Gas CalculationsFree-style Gas Calculations

Treat every problem as a conversion Treat every problem as a conversion problem with the ratio of the change being problem with the ratio of the change being a correction factor.a correction factor.

You must decide if each change will result You must decide if each change will result in an increase or decrease. in an increase or decrease.

Example Problem: What will be Example Problem: What will be the new volume of 6 ftthe new volume of 6 ft33 of gas if of gas if

the following changes are the following changes are made?made?

2.4 atm changed to 6.3 atm2.4 atm changed to 6.3 atm

Heated from 20 Heated from 20 ooC to 300 C to 300 ooCC

5.2 moles changed to 12.6 moles5.2 moles changed to 12.6 moles

Chapter 13 assignmentChapter 13 assignment

Chapter questions on pages 452-453 Chapter questions on pages 452-453 (1– 19, 23, 24)(1– 19, 23, 24)

Problem Bank problems on pages Problem Bank problems on pages 454 – 455 (27, 29, 31, 37, 39, 41, 42, 44, 454 – 455 (27, 29, 31, 37, 39, 41, 42, 44, 52, 54) note that the answers are on page 52, 54) note that the answers are on page 944944

You must show your work for credit.You must show your work for credit.