Behavior of GasesCh 12 – Prentice Hall

Kinetic Theory• Gases are composed of SMALL,

SEPARATE particles called MOLECULES.

• Gas molecules are in CONSTANT MOTION

• All COLLISIONS between particles are PERFECTLY ELEASTIC

• The MOLECULES of a gas display no ATTRACTION or REPULSION for one another.

Kinetic Theory

• The AVERAGE KINETIC ENERGY of the molecules is DIRECTLY PROPORTIONAL to the KELVIN temperature of the gas.

Ideal Gas

• Gas whose BEHAVIOR conforms to the KINETIC THEORY -it is THEORETICAL.

Gas Pressure:

Pressure = FORCE ÷ AREA = ____ atm

Atmospheric Pressure - the PRESSURE the earth’s ATMOSPHERE exerts due to its WEIGHT.

Barometer: Instrument used to measure �ATMOSPHERIC PRESSURE Invented by � TORRICALLI

The Combined Gas Law

Combines the following laws and equations together:

Charles law

Variation of gas volume with temperature while pressure is kept constant

V1/T1 = V2/T2

T (K) = t (0C) + 273.15

Temperature must bein Kelvin

P1V1 = P2V2Boyle’s Law

Constant temperatureConstant amount of gas

Pressure and volume units can be any variant of pressure and volume

HOWEVER the units MUST agree for both pressures and both volumes!

Combined Gas Law

• Expresses the relationship between the PRESSURE, VOLUME and TEMPERATURE of a FIXED amount of GAS.

Equation: P1V1 = P2V2

T1 T2

STANDARD TEMPERATURE AND PRESSURE

• STP CONDITIONS

• 273 K

• 1 atm = 760 mmHg

Combined Gas LawEx: A sample of gas has a volume of 201 L when its

temperature is 293 K and its pressure is 224 mmHg. What volume will the gas occupy at STP?

V1 = 201 L V2 = ?T1 = 293 K T2 = 273 KP1 = 224 mmHg P2 = 760 mmHg

(224) (201) = (760) x (293) (273)

(224) (201) (273) = (293) (760) x

X = 55 L

Diffusion The � RAPID spreading of a GAS

Graham’s Law of Diffusion

Under the same conditions of �TEMPERATURE and PRESSURE, gases DIFFUSE at a rate INVERSLEY proportional to the SQUARE ROOT of their DENSITIES (or MOLAR MASS)

Equation:

Ideal Gas Equation

Equation: PV = nRT • New variables:n = AMOUNT of gas in MOLES R = UNIVERSAL GAS CONSTANT* PROPORTIONALLY constant* value depends on UNITS used for

PRESSURE and VOLUME* value of R when using kPa and LR = 8.314 L . kPa / Mol . K

Ex: The average lung capacity for a female student is 3.9 L. At normal body temperature, 37oC, and 110 kPa, how many moles of air could her lungs hold?

P = 110 kPa V = 3.9 L T = 310 K (273 + 37)

n = X R = 8.314 L . kPa / Mol . K

(110)(3.9) = x (310)(8.314)

(110)(3.9) = 0.17 mol(310)(8.314)

Avogadro’s Law

• Equal VOLUMES of different GASES under the SAME conditions have the SAME number of PARTICLES.

• Conversely, if samples of DIFFERENT GASES at the same TEMPERATURE and PRESSURE contain the SAME number of PARTICLES, then the VOLUMES of all the SAMPLES must be EQUAL.

• At STP, one MOLE of any gas occupies a VOLUME of 22.4 L.

• 22.4 L is the MOLAR VOLUME of a gas.

Dalton’s Law of Partial Pressures

• The PRESSURE of a gas MIXTURE is the SUM of the INDIVIDUAL PRESSURES of each gas ALONE.

Equation: PT = P1 + P2 + P3 …

• Ex: Oxygen gas has been collected over water at a total pressure of 95.0 kPa and a temperature of 25oC. What is the pressure of the dry oxygen gas?

PT = 95 kPa P vapor = 3.17 kPa P oxygen = X

95 = 3.17 + x

91.83 kPa = x

Backdrops:

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