Do Now & AnnouncementsTurn in Gas Laws Demos WorksheetBRING IN A SODA BOTTLE!

Gas Laws Test MON 2/2, TUES 2/3

Scuba Diving Case Study due WED 2/4, THURS 2/5

Variables that Define a Gas Volume (V) - may be expressed in liters,

milliliters, cm3, dm3. Temperature (T) – Always expressed in

Kelvin!!!! (oC + 273 = Kelvin)

Note: Standard Temperature= 273 K Number of Moles (n) - how many

particles are present in the sample of gas

Collisions Cause Pressure

The force per unit area on a surfaceExerted by all gases on any surface

they collide withUnits of pressure:Pascal, Millimeter of mercury, Torr,

Atmosphere STANDARD PRESSURE:

1atm = 760mmHg = 760 torr = 101.3 kPa = 1.01x105 Pa

Pressure-

PressureBarometer-• used to measure atmospheric pressure

The higher the altitude the __________ the atmospheric pressure and the _________ the height of the mercury in the barometer

lowerlower

Whatever the height is, that is your pressure

Measuring Pressure of a Gas

Manometer-

• measures the pressure of an enclosed sample

•Can be open or closed

Whatever the height difference is, that is your pressure in mmHg

Closed Manometer

Pressure

Gas pressure is less than atmospheric pressure when the height of the liquid in the manometer is higher on the _______________. Therefore you will ________________ the height and the atmospheric pressure.

Open Manometer

-h+h

left side of the Usubtract

Examples1. If the atmospheric pressure is 757.8mmHg, what is the pressure of the gas in each of the following manometers?

Dalton’s Law

1) the total pressure exerted by a mixture of gases is the sum of the individual pressures of each gas and

2) each individual gas behaves as if it were independent of the others.

Ptotal = P1 + P2 + P3 + …

Examples

1. Two gases such as oxygen and nitrogen are present in a flask at the following pressures. When combined, what is the pressure of the flask?

PNitrogen =250. mm Hg

POxygen=300. mm Hg

Examples2. Neon gas has a pressure of 1.49atm

in its container. When added to a container holding helium gas the total pressure is 2.34atm. What is the pressure of the helium gas?

Dalton’s Law

Water displacement of gas:Gases given off from the rxn travel

through the tube and into the adjacent container for collection

Gas is impure and contains some water vapor

Patm = Pgas + PH2O

Value depends on temperature

Dalton’s Law Examples A 250 mL sample of oxygen is collected over water at 25°C

and 760 torr pressure. What is the pressure of the dry gas alone? The vapor pressure of water at 25°C is 23.8 torr.  

Oxygen gas from the decomposition of potassium chlorate was collected by water displacement. The barometric pressure and the temperature during the experiment were 731.0torr and 20.0˚C respectively. What was the partial pressure of the oxygen collected? The vapor pressure of water at 20°C is 17.5 torr

   Some hydrogen gas was collected over water at 20.0 ˚C.

The partial pressure of hydrogen is 742.5 torr. What is the barometric pressure of the gas? The vapor pressure of water at 20°C is 17.5 torr

Graham’s Law of Diffusion

Under ideal conditions, the rates at which different gases diffuse (spread out) are inversely proportional to their molar masses.

The rate of effusion and diffusion depend upon

the velocity (speed) of the gas molecules

Graham’s LawSpeed is dependent upon molar

massIn other words, larger gas

molecules will move slower than smaller gas molecules.

Graham’s Law Examples

i. Compare the rates of diffusion of H2 and O2 gases at the same temperature and pressure.

ii. Rank the following gases from slowest to fastest rate of diffusion: H2, CO2, Ne, H2S.

Avogadro’s Law• The volume of a gas under constant temperature

and pressure conditions is directly proportional to the number of moles of gas.

• 1 mole of gas at STP = 22.4 Liters

Boyle’s LawP1V1= P2V2

Inversely proportionalAs the pressure decreases, the

volume increases (temp. constant)

Charles’s Law

Directly proportionalAs temperature increases volume

increases (pressure constant)Temperature must be converted to Kelvin!!!

Gay-Lussac’s Law

Directly ProportionalAs pressure increases

temperature increases (volume constant)

Temperature always in Kelvin Scale

Combined Gas Law

Relates pressure, temperature, and volume in one equation

Temperature must be converted to Kelvin!!!

2

22

1

11

T

VP

T

VP

Ideal Gas Law

PV=nRT n= # molesR=universal gas constant

To determine which R to use in your equation you have to look at the _____________.

R is the universal gas constant.

KmolLmmHg

KmolLkPa

KmolLatm

4.62315.80821.0R

Will be GIVEN on tests/quizzes!

Pressure units being used!!

Temperature must be converted to Kelvin!!!

Solving Gas Laws QuestionsDetermine your known variables and

convert temperature to Kelvin if necessary

Identify the unknown (what are you trying to find?)

Identify the appropriate gas laws formula to use

Plug in your values and solve

Gas Laws Practice Final Answers1) 3.27 atm2) 8.2 L3) 146.5 K4) 60.0 L5) 17.7 L