11Mr. ShieldsMr. Shields Regents Chemistry Regents Chemistry U05 L03 U05 L03

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Properties of GasesProperties of Gases

(1)(1)A gas has VOLUME AND MASSA gas has VOLUME AND MASS

(2) The DENSITY of a gas is considerably LESS than(2) The DENSITY of a gas is considerably LESS than either a solid or liquideither a solid or liquid

(3) The density of a gas is affected by TEMPERATURE(3) The density of a gas is affected by TEMPERATUREAND PRESSUREAND PRESSURE

(4) A gas neither DEFINITE SHAPE NOR VOLUME(4) A gas neither DEFINITE SHAPE NOR VOLUME

Let’s go over the properties of gases again:Let’s go over the properties of gases again:

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Properties of GasesProperties of Gases

(5) There is (5) There is NO PERMANENT ATTRACTIONNO PERMANENT ATTRACTION between between one gas molecule and the nextone gas molecule and the next

(6) Gases MOVE EASILY through one another to(6) Gases MOVE EASILY through one another to form homogeneous solutionsform homogeneous solutions

(7) Gases exert PRESSURE(7) Gases exert PRESSURE

(8) Gas Pressure is affected by TEMPERATURE(8) Gas Pressure is affected by TEMPERATURE

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Properties of GasesProperties of GasesTo understand why gases have these properties To understand why gases have these properties We need to understand something calledWe need to understand something called

This theory was developed by a number of scientistsThis theory was developed by a number of scientistsover a long period of time. over a long period of time. KMT is used to explain the KMT is used to explain the behavior of Gases behavior of Gases as well as Liquids and solidsas well as Liquids and solids. We . We will use it only in connection with gases.will use it only in connection with gases.

the the Kinetic Molecular Theory.Kinetic Molecular Theory.

The KMT was developed to explain what happened onThe KMT was developed to explain what happened onA A molecular scalemolecular scale what earlier scientists observed what earlier scientists observedOn a On a macro scale.macro scale. These macro observations lead toThese macro observations lead toSeveral laws before KMT was established.Several laws before KMT was established.

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Early ScientistsEarly Scientists

So, who were these earlier scientists?So, who were these earlier scientists?

Robert Boyle (1627 – 1691)Robert Boyle (1627 – 1691)

- Boyle’s law (1662)- Boyle’s law (1662)- Explains the - Explains the Pressure-VolumePressure-Volume relationship relationship- - PV=kPV=k

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Early ScientistsEarly Scientists

Jacques Charles (1746 – 1823)Jacques Charles (1746 – 1823)

- Charle’s Law (1787)- Charle’s Law (1787)- - Vol vs.TempVol vs.Temp relationship relationship - - V/T = kV/T = k

Joseph Gay-Lussac (1778 – 1850)Joseph Gay-Lussac (1778 – 1850)

-- Gay-Lussac’s Law (abt 1807) Gay-Lussac’s Law (abt 1807)- - Pressure vs. TempPressure vs. Temp relationship relationship- - P/T = kP/T = k

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Early ScientistsEarly Scientists

John Dalton (1766 – 1844)John Dalton (1766 – 1844)

- The same Dalton who proposed atoms exist- The same Dalton who proposed atoms exist- - Law of Partial PressuresLaw of Partial Pressures (abt. 1801) (abt. 1801)

- - P P TotalTotal = P = Pgas1gas1 + P + Pgas2gas2 + P + Pgas3gas3 + … + …

Amedeo Avogadro (1776 – 1856)Amedeo Avogadro (1776 – 1856)

- The same Avogadro who proposed - The same Avogadro who proposed Equal vol. of gases contains equalEqual vol. of gases contains equal nos. of moleculesnos. of molecules- - Volume vs. no. of particlesVolume vs. no. of particles relationship relationship- - V/n = kV/n = k

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Early ScientistsEarly ScientistsThomas Graham (1805 – 1869)Thomas Graham (1805 – 1869)

- Graham’s law of effusion (1846)- Graham’s law of effusion (1846)- - Rate of effusionRate of effusion is inversely is inversely proportional it’s molecular weightproportional it’s molecular weight- - EffEffgas1gas1 = 1/(M = 1/(M gas1gas1))1/21/2

These early scientists looked at the These early scientists looked at the macro propertiesmacro propertiesof gases. Do you know why this was a Topic?of gases. Do you know why this was a Topic?

Hint:Hint:What “powered” the What “powered” the industrial revolution?industrial revolution?

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Power from steamPower from steam

This is one common example of the useThis is one common example of the useOf power derived from steam Of power derived from steam

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Development of Development of KMTKMTDaniel Bernoulli (1700 – 1782)Daniel Bernoulli (1700 – 1782)

1734 - 1734 - Suggested that the pressure exerted Suggested that the pressure exerted by a gas on the walls of its container is by a gas on the walls of its container is the sum of the many the sum of the many collisionscollisions by by individual molecules all moving individual molecules all moving independently of each otherindependently of each other

James Maxwell (1831 – 1879)James Maxwell (1831 – 1879)

1866 – 1866 – Determined that the Determined that the Avg. velocityAvg. velocity of of molecules = (3RT/M)molecules = (3RT/M)1/21/2

M= Mol. mass, R= gas const, T= Temp(K)M= Mol. mass, R= gas const, T= Temp(K)

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Development of KMTDevelopment of KMT

Rudolph Clausius (1822 – 1888)Rudolph Clausius (1822 – 1888)

18551855- Heat can never travel from cold- Heat can never travel from coldto hot. It always travels from to hot. It always travels from hot to coldhot to cold

18571857- Molecules move with speeds - Molecules move with speeds much fastermuch faster than than the magnitude of the bulk fluid (macro) velocitythe magnitude of the bulk fluid (macro) velocity

18581858- Introduces the concept of - Introduces the concept of MEAN FREE PATHMEAN FREE PATHThe mean The mean distance a molecule travelsdistance a molecule travels before beforeCollision with another moleculeCollision with another molecule

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Development of KMTDevelopment of KMT

Ludwig Boltzman (1844 – 1906)Ludwig Boltzman (1844 – 1906)

18711871- Maxwell-Boltzmann Theory- Maxwell-Boltzmann Theory

Developed in conjunction with Developed in conjunction with James MaxwellJames Maxwell

Molecules have a specific Molecules have a specific distribution of velocitiesdistribution of velocitiesat a at a givengiven temp temp

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Development of KMTDevelopment of KMTWe’ve looked at some of the historical developmentsWe’ve looked at some of the historical developmentsbehind the understanding of gas behavior. Thisbehind the understanding of gas behavior. Thisunderstanding lead to the Kinetic Molecular Theory.understanding lead to the Kinetic Molecular Theory.

We now need to discuss what typically are consideredWe now need to discuss what typically are consideredthe 5 key assumptionsthe 5 key assumptions of the KMT: of the KMT:

1.1. Gas particles do not attract or repel one anotherGas particles do not attract or repel one another2.2. The volume occupied by Gas particles is negligiblyThe volume occupied by Gas particles is negligibly

small compared to the overall volumesmall compared to the overall volume3. Gas Particles are in constant random straight line motion3. Gas Particles are in constant random straight line motion4. No KE is lost when gas molecules collide with each other4. No KE is lost when gas molecules collide with each other5. The avg. KE of all gases is directly proportional to Temp5. The avg. KE of all gases is directly proportional to Temp in Kelvinin Kelvin

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