The Gas Laws

PressureLiquid pressure – exerted equally in

all directions- swimmers feel an increase in pressure as they go deeper down into the ocean

PressureAtmospheric Pressure – (air pressure,

barometric pressure)- at sea level, air pressure = weight of a kg mass on every square centimeter of surface exposed to it** we are not conscious of air pressure because it is exerted in all directions

Measuring PressureHg Barometer – measures AIR

PRESSURE- Pressure varies with altitude

- Decrease in air pressure as you increase altitude

- Drop in air pressure before a storm- Normal Atmospheric Pressure - 760

mmHg or 1atm

Measuring Pressure• 1 Atm = 760 mm Hg = 760 Torr=

101.3 kPa

Measuring PressureManometer – measures pressure exerted by a gas in a

closed container- 2 types – closed and open

Measuring PressureClosed Tube Manometer

Gas LawsWe will be studying the behavior of

gases under varying conditions including:

Pressure, Volume and TemperatureWatch Safari Montage video - Common Properties of Gases

http://econtent2.bucksiu.org/SAFARI/montage/play.php?frompage=play&keyindex=3139&location=local&chapterskeyindex=22429&sceneclipskeyindex=-1

Kinetic Theory of Gases

• Gas is made up of very small particles that are in constant random motion

• Gas particles are free to spread far apart from each other

• The higher the temperature – the faster the particles move

Boyle’s Law•Safari Montage Video – Boyles Law

http://econtent2.bucksiu.org/SAFARI/montage/playlistedit.php?playlisttype=MY&Action=MakeActive&playlistkeyindex=978&location=local

• At constant temperature, the volume of a gas varies inversely with pressure

P1V1 = P2V2

Boyle’s Law•Safari Montage Video – Boyles Law

http://econtent2.bucksiu.org/SAFARI/montage/playlistedit.php?playlisttype=MY&Action=MakeActive&playlistkeyindex=978&location=local

• At constant temperature, the volume of a gas varies inversely with pressure

P1V1 = P2V2

Boyle’s LawEx: What is the final pressure of 25.0 ml of a gas that was

originally 38.3ml at a pressure of 765 mmHg?

Charles’ Law• http://econtent2.bucksiu.org/SAFARI/montage/play.php?

keyindex=3139&chapterskeyindex=22438&keyconceptskeyindex=74460&sceneclipskeyindex=-1&location=local

At constant pressure, volume and temperature are directly related.

V1 = V2 or V1T2 = V2T1

T1 T2

*** Temp. MUST be in Kelvin

Charles’ LawEx: A balloon at 27.3 oC has a volume of 4.0 L. It is then

heated to a temperature of 57.0 oC. What is the new volume of the balloon?

Gay-Lussac’s Law• http://econtent2.bucksiu.org/SAFARI/montage/play.php?

keyindex=3139&chapterskeyindex=22438&keyconceptskeyindex=74460&sceneclipskeyindex=-1&location=local

• At constant volume, pressure and temperature are DIRECTLY related

P1 = P2 or P1T2 = P2T1

T1 T2

*** Temp. MUST be in Kelvin

Gay-Lussac’s LawEx: A gas is left in a used aerosol can is at a pressure of

1.0 atm at 27.0 oC. If this can is thrown onto a fire, what is the internal pressure of the gas when it reaches 927 oC?

Combined Gas LawThe three laws we have learned can be combined into a

single expression:

P1V1 = P2V2 or P1V1T2 = P2V2T1

T1 T2

** Where temperature MUST be in Kelvin

Combined Gas LawEx: A cylinder of compressed oxygen has a volume of

30.0L and 100.0 atm pressure at 27 oC. The cylinder is cooled until the pressure is 5.0 atm and the volume is 50 L. What is the new temperature of the gas?

Ideal Gas Lawhttp://econtent2.bucksiu.org/SAFARI/montage/play.php?

keyindex=3139&chapterskeyindex=22438&keyconceptskeyindex=74448&sceneclipskeyindex=-1&location=local

Ideal Gas – follows all the gas laws at ALL conditions of pressure and temperature. - Does not really exist.- Real gases usually start to liquefy at low temp. and high pressures.- We will use ideal gases for all problems in this class – therefore we will now learn the Ideal Gas Law

Ideal Gas Law - Number of moles (n) is directly related to the volume of

a gas

PV = nRTWhere: P = pressure

V = volumen = number of molesR = ideal gas constantT = temperature (Kelvin)

Ideal Gas LawR = ideal gas constant

- number depends on the units of P,V and T 0.0821 L . Atm

K . Mol

62.4 L. mmHgK. mol

8.31 L.kPaK.mol

Ideal Gas LawEx: A rigid hollow sphere of helium (680 L) is heated to

600K. The pressure increased to 18 atm. How many moles of helium does the sphere contain?

Ideal Gas LawEx: What is the pressure of 25.0 g of carbon dioxide that

occupies a volume of 350 ml at 25 oC?

Dalton’s Law of Partial Pressure

Ex: What would be the pressure inside a cylinder if we combined these three gases?

Dalton’s Law of Partial Pressure

At constant volume and temperature, the pressure exerted by a mixture of gases is equal to the sum of the partial pressures.

PT = P1 + P2 + P3 + …

Dalton’s Law of Partial Pressure

Ex: Air contains oxygen, nitrogen, carbon dioxide and trace amounts of other gases. What is the partial pressure of the oxygen gas given the following information?P of nitrogen = 593.4 mmHgP of carbon dioxide = 0.3 mmHgP of trace gases = 7.1 mmHgTotal air pressure = 760 mmHg

Graham’s Law of Diffusion

Diffusion – movement of particles

Which do you think would travel faster? A light gas (such as H) or a heavy gas (such as CO2)

Graham’s Law of Diffusion

Law says – rate of diffusion of a gas is inversely proportional to the square root of its formula mass.

In other words: Lighter gas travel faster!!!!!

Mathematically written:

Rate A = √MB

Rate B √MA

Graham’s Law of Diffusion

Ex: Which gas travels faster: CH4 or O2?

Ex: How much faster does steam travel than carbon dioxide?