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The Behavior of Gases

1. Describe the properties of gas particles (according to the kinetic theory).

2. Explain how the kinetic energy of gas particles relates to Kelvin temperature. What happens to these particles as the average KE changes?

3. What are some variables/factors that would impact a gases behavior?

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Assumptions of the Kinetic Theory of Gases (Review!)

1. The volumes of individual gas particles are very small in relation to the distances between them. Thus, there is a large amount of empty space between gas particles.

2. There are no attractive or repulsive forces existing between particles. Thus, gas particles move about in an independent fashion, occupying the full volume of their container.

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3. Gas particles tend to be in constant motion, traveling in straight paths until chance collisions with other particles or a wall alters their course.

4. Collisions between gas particles are perfectly elastic, that is, kinetic energy is transferred without loss from one particle to another.

5. The average kinetic energy of the gas particles is directly proportional to Kelvin temperature.

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Variables that Describe a Gas

Pressure (P) – kPa, atm or mm Hg

(1 atm = 760 mm Hg = 101.3 kPa)

Volume (V) – L (liters)

Temperature (T) – K (Kelvin)

K = 273 + °C Number of moles (n)

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Chapter 11: Gases Kinetic Molecular Theory:

particles constantly in motion

Avg. KE, temperature, pressure, volume and amount of a gas all related

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Air Pressure & Force

Air Pressure due to the collision of molecules on surfaces

Pressure = defined as the force per unit area on a surface

Pressure =

Force unit: newton (N)

Force

Area

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The Barometer

Pressure depends on area of contact; smaller area, greater pressure

• Atmosphere exerts pressure - total of individual gas pressures (mostly N, then O)

• Measured using barometers

• Units/values/CF’s

(ie. 1 torr = 1 mmHg)

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Dalton’s Law of Partial Pressures

Partial pressures are exerted by individual gases

Law states that total pressure of a gas mixture is the sum of the component pressures

PT = P1+P2+P3…

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Boyle’s Law

The 5 Ga s La ws

There are relationships (direct and indirect) between pressure,

temperature and volume (as well as with the # of moles n.)

The 5 gas laws take all of these relationships into account.

1) Boyle’s Law

2) Charles’s Law

3) Gay-Lussac’s Law (really)

4) The Combined Gas Law

5) The Ideal Gas Law

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Boyle’s LawInversely relates pressure and volume.

P1V1=P2V2

In Boyle’s Law, pressure and volume are inversely related.

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Charles’s LawDirectly relates volume and temperature

V1 = V2

T1 T2

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Gay-Lussac’s LawDirectly relates pressure and temperature

P1/T1=P2/T2

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Combined Gas LawEquation?

P1V1 = P2V2

T1 T2

Ideal Gas LawAllows for us to also solve for moles (n) within a gas

PV = nRTwhere R is a constant (0.0821 Lxatm/molxK)

Examples1) A sample of gas at 47°C and 1.03 atm occupies a

volume of 2.20 L. What volume would this gas

occupy at 107°C and 0.789 atm?

Q: Which Gas Law? A:

Examples2) To what temperature must a sample of nitrogen at

27°C and 0.625 atm be taken so that it’s pressure

becomes 1.125 atm at constant volume?Q: Which Gas Law? A:

Examples3) A meteorological balloon contains 250.0 L He at

22°C and 740.0 mm Hg. What volume will it occupy

at an altitude at which the temperature is -52°C and

the pressure is 0.750 atm?

(hint: notice the differing units of pressure)Q: Which Gas Law? A:

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Graham’s Law of Effusion

Basically states that the rates of a gases effusion (?) at the same temperature and pressure is inversely proportional to the square roots of their molar masses EXPLAIN…

Square root of Molar Mass A/Square root of Molar Mass B

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Avogadro’s LawStates that equal volumes of gases at the same

temperature and pressure contain equal number of

molecules. (and remember that the magic number for

volume of one mole of any gas at STP is… )22.4 L

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Quiz!

Find the mass of each of the following: A) 5.60L O2 at 1.75 atm and 250.0K

B) 3.50 L NH3 at 0.921 atm and 27°C

C) 125 mL SO2 at 0.822 atm and -5°C