GasesGases

Characteristics of GasesCharacteristics of Gases

Gases are Gases are fluidsfluids– In other words, they can In other words, they can flowflow..

Gases have Gases have lowlow density density– Most of the Most of the volumevolume occupied by gases occupied by gases

are are emptyempty space. space. Gases are highly Gases are highly compressiblecompressible CompletelyCompletely fills a container fills a container

PressurePressure Pressure is defined as the Pressure is defined as the forceforce

divided by divided by areaarea.. So, it is the So, it is the forceforce on an on an areaarea.. That is why scientists derived the That is why scientists derived the

pascalpascal to measure pressure. to measure pressure. A A pascalpascal is defined as one is defined as one newtonnewton

(the SI unit for force) applied over an (the SI unit for force) applied over an area of area of oneone square square metermeter..

Pressure is caused when a gas Pressure is caused when a gas collidescollides with the with the wallswalls of a container. of a container.

CollisionsCollisions = = forceforce, container walls give , container walls give us the us the areaarea over which the force is over which the force is appliedapplied

How do we measure How do we measure pressure?pressure?

One way is with One way is with a a barometerbarometer

The most The most common type common type use a use a liquidliquid to to measure the measure the atmospheric atmospheric pressure.pressure.

How is pressure recorded?How is pressure recorded? There are several different pressure units There are several different pressure units

that can be used.that can be used.UnitUnit AbbreviationAbbreviation Equivalent number Equivalent number

of pascalsof pascals

AtmosphereAtmosphere atmatm 1 atm = 101,325 Pa1 atm = 101,325 Pa

BarBar barbar 1 bar = 100,0251 bar = 100,025

Millimeter of Millimeter of mercurymercury

mm Hgmm Hg 1 mm Hg = 133.3221 mm Hg = 133.322

PascalPascal PaPa 11

Pounds per square Pounds per square inchinch

psipsi 1 psi = 6.89286 x 1 psi = 6.89286 x 101033 Pa Pa

TorrTorr torrtorr 1 torr = 133.3221 torr = 133.322

Example problemsExample problems

Convert each of the following Convert each of the following pressures into the specified unit.pressures into the specified unit.

72.7 atm 72.7 atm pascals pascals 12.33 kPa 12.33 kPa millimeters of mercury millimeters of mercury

(hint kPa means 1000 Pa)(hint kPa means 1000 Pa) 100.0 kPa 100.0 kPa atmospheres atmospheres 44.7 psi 44.7 psi pascals pascals

AnswersAnswers

7366327.5 pascals7366327.5 pascals 92.5 millimeters of mercury 92.5 millimeters of mercury 0.987 atmospheres0.987 atmospheres 308196 pascals308196 pascals

Kinetic Molecular TheoryKinetic Molecular Theory

Book Definition - A Book Definition - A theorytheory that that explains that the explains that the behaviorbehavior of physical of physical systems depends on the systems depends on the combinedcombined actions of the actions of the moleculesmolecules constituting constituting the system.the system.

Another way to say this – the Another way to say this – the behaviorbehavior of a of a systemsystem depends on the depends on the actionsactions of the of the moleculesmolecules that make it that make it up.up.

Concepts of the Kinetic Concepts of the Kinetic Molecular TheoryMolecular Theory

All matter is composed of All matter is composed of particlesparticles.. All matter is in All matter is in constant constant motionmotion Gases particles are in Gases particles are in constantconstant, , rapidrapid, ,

and and randomrandom motion motion This motion represents the This motion represents the kinetickinetic energy energy

(KE = ½ mv(KE = ½ mv22) of the system.) of the system. Particles of a gas are Particles of a gas are veryvery farfar apart apart

relative to their size.relative to their size. All collisions are perfectly All collisions are perfectly elasticelastic. In other . In other

words, there is words, there is nono loss or gain in energy. loss or gain in energy.

Temperature and Kinetic Temperature and Kinetic EnergyEnergy

The average kinetic energy of random The average kinetic energy of random motion is motion is proportionalproportional to the absolute to the absolute temperature (temperature in Kelvin)temperature (temperature in Kelvin)

So, if the temperature changes; So, if the temperature changes; the the random motion changes.random motion changes.

If temperature If temperature increasesincreases; random ; random motion motion increasesincreases..

Note: this does not mean that all Note: this does not mean that all particles are moving at the particles are moving at the samesame speed, speed, but overall the rates but overall the rates increaseincrease the the average.average.

HomeworkHomework

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