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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