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GasesGases

The Gas LawsThe Gas Laws

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Properties of GasesProperties of Gases No fixed shape or volumeNo fixed shape or volume Molecules are very far apart and in a Molecules are very far apart and in a

state of constant rapid motionstate of constant rapid motion Can be compressedCan be compressed There are weak attractive forces There are weak attractive forces

between moleculesbetween molecules

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TemperatureTemperature Measure of average velocity(speed) of Measure of average velocity(speed) of

moleculesmolecules 0 kelvins = -273 0 kelvins = -273 00C(absolute zero) all C(absolute zero) all

molecular motion stops at this molecular motion stops at this temperaturetemperature

__T kelvins = ____T kelvins = __00C + 273C + 273 -50 -50 00C = _______KC = _______K 80 80 00C = _______ KC = _______ K 300 K = _______ 300 K = _______ 00 C C

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PressurePressure Force per unit area. P=F/A N/mForce per unit area. P=F/A N/m22

Gas molecules fill container.Gas molecules fill container. Molecules move around and hit Molecules move around and hit

sides.sides. Collisions are the force.Collisions are the force. Container has the area.Container has the area. Measured with a barometer.Measured with a barometer.

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Gas PressureGas Pressure Measured in Pascal (Pa) or Measured in Pascal (Pa) or

Kilopascals (KPa)Kilopascals (KPa) 1000 Pa = 1 KPa1000 Pa = 1 KPa 1 Pascal = 1N/m1 Pascal = 1N/m22

1 standard atmosphere = 1 atm 1 standard atmosphere = 1 atm 1atm = 101.3 KPa = 760 mm Hg1atm = 101.3 KPa = 760 mm Hg 1 atm = 760 torr = 101.3 KPa1 atm = 760 torr = 101.3 KPa 1 torr = 101.3/ 760 KPa1 torr = 101.3/ 760 KPa

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Standard Temperature and Standard Temperature and PressurePressure

When temperature is 0 When temperature is 0 00C or 273 C or 273 Kelvins, pressure is 101.3 KPa – this Kelvins, pressure is 101.3 KPa – this is known as standard temperature is known as standard temperature and pressure or STP. and pressure or STP.

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BarometerBarometer The pressure of the The pressure of the

atmosphere at sea atmosphere at sea level will hold a level will hold a column of mercury column of mercury 760 mm Hg.760 mm Hg.

1 atm = 760 mm Hg1 atm = 760 mm Hg

1 atm Pressure

760 mm Hg

Vacuum

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ManometerManometer

Gas

h

Column of Column of mercury to mercury to measure measure pressure.pressure.

h is how much h is how much lower the lower the pressure is pressure is than outside. than outside.

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ManometerManometer h is how much h is how much

higher the gas higher the gas pressure is than pressure is than the atmosphere.the atmosphere.

h

Gas

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Ideal Gas LawIdeal Gas Law PV = nRTPV = nRT P= pressure in KPaP= pressure in KPa V= volume in LV= volume in L n= moles n= moles R = constant 8.31 LxKPa/molxKR = constant 8.31 LxKPa/molxK T = temperature in Kelvins. T = temperature in Kelvins.

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Ideal Gas ( page 483)Ideal Gas ( page 483) A hypothetical substance - the ideal A hypothetical substance - the ideal

gasgas Molecules are dimensionlessMolecules are dimensionless Molecules are in constant motionMolecules are in constant motion Collisions are elastic (no energy lost)Collisions are elastic (no energy lost) No attractive forces in moleculesNo attractive forces in molecules http://www.youtube.com/watch?http://www.youtube.com/watch?

v=BxUS1K7xu30&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr&index=13v=BxUS1K7xu30&list=PL8dPuuaLjXtPHzzYuWy6fYEaX9mQQ8oGr&index=13

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ExampleExample Example 1 – A sample of oxygen gas Example 1 – A sample of oxygen gas

occupies 5.6 L at STP. How many grams occupies 5.6 L at STP. How many grams of oxygen are present?of oxygen are present?

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Example 2Example 2 Calculate the pressure of 1.75 g of Calculate the pressure of 1.75 g of

helium gas at 16.0 helium gas at 16.0 00C occupying C occupying 3.25 L.3.25 L.

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Answers to WorksheetAnswers to Worksheet 1. 24000 mol1. 24000 mol 2. 1.3g2. 1.3g 3. 9.1L3. 9.1L 4. 90g4. 90g 5. 13L5. 13L 1. 9.9 mol 2. 3.5x101. 9.9 mol 2. 3.5x103 3 3. 2.8 x103. 2.8 x1044

4. 2.4x104. 2.4x1022 mol 5. 406.2 K, 133.2 mol 5. 406.2 K, 133.2 00CC

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Molar Volume of GasesMolar Volume of Gases Equal volumes of all gases at equal Equal volumes of all gases at equal

temperature and pressure contain same temperature and pressure contain same number of particles.(Avogadro’s number of particles.(Avogadro’s hypothesis)hypothesis)

Draw diagrams hereDraw diagrams here 1mole = 6.02 x 101mole = 6.02 x 102323 particles of gas particles of gas The volume must be the same for all The volume must be the same for all

gasesgases Molar volume = volume occupied by 1 Molar volume = volume occupied by 1

mole of gasmole of gas

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Molar VolumeMolar Volume Molar volume of any gas is Molar volume of any gas is 22.4L22.4L at at

STP 0STP 0ooC and 101.3KPaC and 101.3KPa Knowing the volume allows you to Knowing the volume allows you to

find the molesfind the moles Molar volume is Molar volume is 24.5L24.5L at NTP (normal at NTP (normal

temperature and pressure) 25temperature and pressure) 25ooC and C and 101.3KPa101.3KPa

At higher temperature the molar At higher temperature the molar volume is expected to be higher.volume is expected to be higher.

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Exception to molar volumeException to molar volume Some gases have molar volume Some gases have molar volume

slightly different than 22.4L because slightly different than 22.4L because of attraction between molecules.of attraction between molecules.

Examples are ClExamples are Cl22 has molar volume has molar volume

of 22.1L and SOof 22.1L and SO22= 21.9L at STP= 21.9L at STP

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ExamplesExamples1.1. What is the molar volume of any gas at STP?What is the molar volume of any gas at STP?

2.2. What is the molar volume of a gas if 0.358 What is the molar volume of a gas if 0.358 moles occupy 8.30L?moles occupy 8.30L?

3.3. What volume will 128 g of methane occupy What volume will 128 g of methane occupy at STP?at STP?

4.4. What volume will 0.219 moles of COWhat volume will 0.219 moles of CO22 occupy occupy

at STP?at STP?

5.5. How many moles of hydrogen are in balloon How many moles of hydrogen are in balloon filled to 5.0L STP?filled to 5.0L STP?

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Molar volume and densityMolar volume and density Molar volume = molar mass/densityMolar volume = molar mass/density Density of gas = molar mass/molar Density of gas = molar mass/molar

volumevolume The density of methanol CHThe density of methanol CH33OH at 20 OH at 20

ooC is 0.813 g/mL. What is the mass C is 0.813 g/mL. What is the mass of 0.500L of alcohol at 20of 0.500L of alcohol at 20ooC?C?

Do #1-3 page 138Do #1-3 page 138

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Answers to Molar volumeAnswers to Molar volume1.1. 7.67L7.67L

2.2. 0.446mol0.446mol

3.3. a)2.80x10a)2.80x1022LL b) 7.84L C) 95.2Lb) 7.84L C) 95.2L

4.4. a)0.0167 mol b) 2.23x10 a)0.0167 mol b) 2.23x10 -4-4molmol

5.5. 5.50g5.50g

6.6. 32.0g32.0g

7.7. 1.43g/L1.43g/L

8.8. 6.05x106.05x102424

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Chemical reactions with gasesChemical reactions with gases Many gases undergo chemical Many gases undergo chemical

reactions reactions 2H2H2(g)2(g) + O + O2(g)2(g)2H2H22OO(g) (g)

2 L of hydrogen gas reacts with 1 L 2 L of hydrogen gas reacts with 1 L of oxygen gas to produe 2 L of waterof oxygen gas to produe 2 L of water

NN2(g)2(g) + 3H + 3H2(g)2(g) 2NH 2NH3(g)3(g)

Volumes of gaseous substances are Volumes of gaseous substances are consumed and produced.consumed and produced.

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Gay-Lussac’s Law of combining Gay-Lussac’s Law of combining VolumesVolumes

Gases combine as volumes and Gases combine as volumes and should be in small whole number should be in small whole number ratios.ratios.

Example: What volume of oxygen Example: What volume of oxygen gas at STP is required for complete gas at STP is required for complete combustion of 4.50L of butane Ccombustion of 4.50L of butane C44HH10. 10.

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ExamplesExamples How many litres of water can be How many litres of water can be

made from 24 grams of oxygen gas made from 24 grams of oxygen gas and 5.0 g of hydrogen gas at STP? and 5.0 g of hydrogen gas at STP? Find Limiting?Find Limiting?

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Gases and StoichiometryGases and Stoichiometry Reactions happen in molesReactions happen in moles At Standard Temperature and At Standard Temperature and

Pressure (STP, 0ºC and 1 atm) 1 Pressure (STP, 0ºC and 1 atm) 1 mole of gas occupies 22.42 L.mole of gas occupies 22.42 L.

If not at STP, use the ideal gas law to If not at STP, use the ideal gas law to calculate moles of reactant or calculate moles of reactant or volume of product.volume of product.

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Mixed StoichiometryMixed Stoichiometry Drano contains Al which reacts with Drano contains Al which reacts with

excess NaOH to produce bubbles of excess NaOH to produce bubbles of hydrogen. How many mL of Hhydrogen. How many mL of H22 will will

be released when 0.150g of Al are be released when 0.150g of Al are dissolved at STP?dissolved at STP?

2Al(s)+ 2NaOH(aq) +2H2Al(s)+ 2NaOH(aq) +2H22O(l)O(l) 3H 3H22(g) (g)

+ 2 NaAlO+ 2 NaAlO22(aq)(aq)

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Answers to worksheetAnswers to worksheet1.1. 864.5L 9.7.0L864.5L 9.7.0L

2.2. 8.8g8.8g 10. 12.9L 10. 12.9L

3.3. 4.28mol 11. 3.55x104.28mol 11. 3.55x102424

4.4. 69.8L69.8L

5.5. 2.66g2.66g

6.6. 2.8x102.8x1055

7.7. 890g890g

8.8. 2.3x102.3x1066

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ExamplesExamples Using the following reactionUsing the following reaction

calaculate the mass of sodium hydrogen calaculate the mass of sodium hydrogen carbonate necessary to produce 2.87 L carbonate necessary to produce 2.87 L of carbon dioxide at 25ºC and 2.00 atm.of carbon dioxide at 25ºC and 2.00 atm.

NaCl(aq) + CO (g) +H O(l)2 2

NaHCO (s) + HCl 3

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The Same reactionThe Same reaction

What mass of HWhat mass of H22O will be produced O will be produced

from 65.0 L of Ofrom 65.0 L of O22 and 75.0 L of NH and 75.0 L of NH33

both measured at STP? both measured at STP? What volume Of NO would be What volume Of NO would be

produced?produced? What mass of NO is produced from What mass of NO is produced from

500. L of NH3 at 250.0ºC and 3.00 atm?500. L of NH3 at 250.0ºC and 3.00 atm?

4NH (g) + 5 O 4 NO(g) + 6H O(g)3 22 ( )g