Chapter 11. Gases. 10. 1 Kinetic Molecular Theory. State the kinetic-molecular theory of matter, and describe how it explains certain properties of matter. List the five assumptions of the kinetic-molecular theory of gases. Define the terms ideal gas and real gas.
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State the kinetic-molecular theory of matter, and describe how it explains certain properties of matter.
List the five assumptions of the kinetic-molecular theory of gases.
Define the terms ideal gas and real gas.
Describe each of the following characteristic properties of gases: expansion, density, fluidity, compressibility, diffusion, and effusion.
Describe the conditions under which a real gas deviates from “ideal” behavior.
Tested ideas about the
movement of particles!
This theory is used to explain the energy and forces that cause the properties of solids, liquids, and gases.
What determines have fast a gas effuses? Mass
KMT applies only to ideal gasses.
Which parts are not true for real gases?
Pressure (P): the force per unit area on a surface.
Pressure = Force
More force on a given area, the greater the pressure.
smaller the area is on which a given force acts, the greater the pressure.
1 atm = 101.3 kPa = 760 mmHg = 760 torr
The average atmospheric pressure in Denver, Colorado is 0.830 atm. Express this pressure in:
a. millimeters of mercury (mm Hg) and
b. kilopascals (kPa)
Given:atmospheric pressure = 0.830 atm
Unknown: a. pressure in mm Hg
b. pressure in kPa
PT = P1 + P2 + P3 + …
Total Pressure = sum of pressures of each individual gas
Patm = Pgas + PH2O
To get Patm, record atmospheric pressure.
KClO3decomposes and the oxygen gas was collected by water displacement. The barometric pressure and the temperature during the experiment were 731.0 torr and 20.0°C. respectively. What was the partial pressure of the oxygen collected?
PT = Patm= 731.0 torr
PH2O = 17.5 torr(vapor pressure of water at 20.0°C, from table A-8 in your book)
Patm = PO2+ PH2O
Patm = PO2+ PH2O
PO2 = Patm- PH2O
Mole fraction of a gas(XA) =
mole fraction: ratio of the number of moles of one component of a mixture to the total number of moles
Moles of gas A (nA)
Total number of moles of a gas
Partial pressures can be determined from mole fractions using the following equation:
P1V1 = P2V2
Variables: pressure & volume
Constant: temperature, amount of gas
A sample of oxygen gas has a volume of 150.0 mL when its pressure is 0.947 atm. What will the volume of the gas be at a pressure of 0.987 atm if the temperature remains constant?
P1 = 0.947 atm P2 = 0.987 atm
V1 = 150.0 mL V2 = ?
K = 273 + °C.
O K = -273 oC
A sample of neon gas occupies a volume of 752 mL at 25°C. What volume will the gas occupy at 50°C if the pressure remains constant?
Temperature must be in KELVIN!!!
V1 = 752 mL V2 = ?
T1 = 25°C T2 = 50°C
The gas in a container is at a pressure of 3.00 atm at 25°C. Directions on the container warn the user not to keep it in a place where the temperature exceeds 52°C. What would the gas pressure in the container be at 52°C?
Temperature must also be in KELVIN!!!
P1 = 3.00 atm P2 = ?
T1 = 25°C T2 = 52°C
P2 = P1T2 = (3.00 atm) (325 K) = 3.27 atm
T1 298 K
Constant: amount of gas
NOTE: P & V are directly related to T, while P is inversely related to V
A helium-filled balloon has a volume of 50.0 L at 25.0°C and 1.08 atm. What volume will it have at 0.855 atm and 10.0°C?
Temperature must be in KELVIN!!
P1 = 1.08 atm P2 = 0.855 atm
V1 = 50.0 L V2 = ?
T1 = 25.0°C T2 = 10.0°C
Because of Avogadro’s law equal volumes of gases at constant temperature and pressure contain equal numbers of molecules.
22.41410 L (rounded to 22.4 L)
Review: Write down the combined gas law; where do you think “n” fits in?
If both sides must equal each other, we can set one side equal to a constant. We’ll call this constant “R.”
What are the standard conditions for an ideal gas?
P = n =
V = T =
Plug in values into the equation and calculate. What is the constant that you get?
Usually rounded to 0.0821 (Latm/molK)
ALWAYS MATCH UP YOUR UNITS!!!!
2H2(g) + O2(g) → 2H2O(g)
2 molecules 1 molecule 2 molecules
2 mole 1 mole 2 mol
2 volumes 1 volume 2 volumes
Number 1 on Practice Sheet
N2 + 3 H2 2 NH3
0.100 mol H2 x 1 mol N2 x 22.4 L N2
3 mol H2 1 mol N2
= 0.747 L N2
V = 350. mL = 0.350 L
n = 0.250 g = ? mol
T = 400 K
P = nRT = .00568 mol (.0821 Latm/molK) 400 K
V .350 L
= 0.533 atm
Number 2 on Practice Sheet
N2 + 3 H2 2 NH3
Note: This system is NOT at STP!!
0.100 mol H2 x 1 mol N2= 0.0333 mol N2
3 mol H2
P = 715 mmHg
V = ?
n = 0.0333 mol N2
R = 62.4 LmmHg/molK
T = 25OC + 273 = 488 K
Graham’s law of effusion:
the rates of effusion of gases at the same temperature and pressure are inversely proportional to the square roots of their molar masses.