Exam 4 Flashcards
why study gases?
1) To gain an understanding of real-world phenomena
2) To gain an understanding of how science “works”
gas
- Uniformly fills any container
- Mixes completely with any other gas
- Exerts pressure on its surroundings
- has small forces between them
barometer
- Device used to measure atmospheric pressure
- Mercury flows out of the tube until the pressure of the column of mercury standing on the surface of the mercury in the dish is equal to the pressure of the air on the rest of the surface of the mercury in the dish
- mm Hg
units of pressure
- Unit millimeters of mercury (mm Hg) is often called the torr
a) The units “torr” and “mm Hg” are used interchangeably - Standard atmosphere (atm): A related unit for pressure
- Pascal: SI unit for pressure (Pa)
- PRESSURE = FORCE / AREA
- SI units = Newton/meter2= 1 Pascal (Pa)
- 1 standard atmosphere = 101,325 Pa
- 1 standard atmosphere = 1 atm= 760 mm Hg = 760 torr
Unit millimeters of mercury (mm Hg) is often called the
torr
what 2 units can be used interchangeably?
torr and mm Hg
Standard atmosphere (atm)
A related unit for pressure
formula for pressure
P = force/area
1 atm = __ mm Hg
760
1 atm = __ torr
760
1 atm = __ Pa
101,325
The pressure of the air in a tire is measured to be 28 psi. Represent this pressure in both torr and pascals.
- 9 atm x 760 torr / 1 atm = 1.4 x 10^3 torr
1. 9 atm x 101325 Pa/ atm = 1.9 x 10^5 Pa
The vapor pressure over a beaker of hot water is measured as 656 torr. What is this pressure in atmospheres?
656 torr x 1 atm / 760 torr = 0.863 atm
Robert Boyle’s Experiment
Study of the relationship between the pressure of the trapped gas and its volume
- when u increase P, you decrease V
- ex: pillow
Boyle’s Law Graph
L shaped curve
- pressure and volume
- inversely proportional
Boyle’s Law
- P1V1 = P2V2
- Pressure and volume are inversely related or inversely proportional
- PV = k
- k is a constant for a given amnt of gas at a specific temp
- V= k/p
- T and moles are constant
A sample of helium gas occupies 12.4 L at 23 °C and 0.956 atm. What volume will it occupy at 1.20 atm assuming that the temperature stays constant?
9.88 L
Graphing Data for Several Gases
- It is easier to write an equation for the relationship between volume and temperature if the lines are extrapolated to the origin of the graph
- Use absolute zero for the temperature
- Absolute zero
absolute zero
temperature of −273 °C beyond which matter cannot be cooled
Charles’s Law Graph
V on y axis and T on x axis
- direct relationship
- straight up
Charles’s Law
- V1/T1 = V2/T2
- Direct proportionality between volume and temperature(in Kelvin) represented by the equation known as Charles’s law
- V = bT (b is a proportionality constant)
- K = °C + 273
- 0 K is called absolute zero
- constant pressure and moles
__ K is called absolute zero
0
Suppose a balloon containing 1.30 L of air at 24.7 °C is placed into a beaker containing liquid nitrogen at –78.5 °C. What will the volume of the sample of air become (at constant pressure)?
0.849 L
Avogadro’s Law
- n1/V1 = n2/V2
- Volume and numbers of moles are directly related (constant T and P)
- V = an (a is a proportionality constant)
- constant temp and pressure
Avogadro’s Law Graph
- direct relationship
- straight up
- volume on y axis and moles on x axis
If 2.45 mol of argon gas occupies a volume of 89.0 L, what volume will 2.10 mol of argon occupy under the same conditions of temperature and pressure?
76.3 L
Ideal Gas Law
- PV = nRT
- R = 0.08206 L atm / mol K
- We can bring all the laws together under one comprehensive law:
a) charles’s law: V =bT (constant P and n)
b) Avogadro’s law: V =an (constant Tand P)
c) Boyle’s law: V= k / P (constant T and n)
what is the universal gas constant?
0.08206 L atm / mol K
An automobile tire at 23 °C with an internal volume of 25.0 L is filled with air to a total pressure of 3.18 atm. Determine the number of moles of air in the tire.
3.27 mol
What is the pressure in a 304.0-L tank that contains 5.670 kg of helium at 25 °C?
114 atm
At what temperature (in °C) does 121 mL of CO2 at 27 °C and 1.05 atm occupy a volume of 293 mL at a pressure of 1.40 atm?
696 °C
Dalton’s Law of Partial Pressures
- For a mixture of gases in a container
a) P total = P1 + P2 + P3 + . . . - the total pressure exerted is the sum of the pressures that each gas would exert if it were alone
- The pressure of the gas is affected by the number of moles of particles present
- The pressure is independent of the nature of the particles
Two Crucial Things to be learned from the Dalton’s Law
1) The volume of the individual particles must not be very important
2) The forces among the particles must not be very important
Collecting a Gas over Water
Total pressure is the pressure of the gas plus the vapor pressure of the water
- However, we need to determine the pressure of the gas and not the mixture collected
- to JUST get the gas, SUBTRACT the water vapor
Consider the following apparatus containing helium in both sides at 45 °C. Initially, the valve is closed.
- After the valve is opened, what is the pressure of the helium gas?
2.25 atm
- 4 L of oxygen gas at 25.0 °C and 1.30 atm and 8.50 L of helium gas at 25.0 °C and 2.00 atm were pumped into a tank with a volume of 5.81 L at 25 °C.
- Calculate the new partial pressure of oxygen
- Calculate the new partial pressure of helium
- Calculate the new total pressure of both gases
new partial pressure of oxygen = 6.13 atm
new partial pressure of helium = 2.93 atm
new total pressure of both gases = 9.06 atm
Scientific Method
- A law is a generalization of observed behavior
- Laws are useful as they help us predict behavior of similar systems
- A model can never be proved absolutely true
- A model is an approximation and is destined to be modified
The Kinetic Molecular Theory of Gases: Basic Postulates of the Kinetic Molecular Theory
in science, “what” always comes before why
implications of the Kinetic Molecular Theory: Meaning of temperature
Kelvin temperature of a gas is directly proportional to the average kinetic energy of the gas particles
implications of the Kinetic Molecular Theory: Relationship between pressure and temperature
Gas pressure increases as the temperature increases because the gas particles move faster and undergo collision more often
implications of the Kinetic Molecular Theory: Relationship between volume and temperature
Volume of a gas increases with temperature because the gas particles speed up
You are holding two balloons of the same volume. One contains helium, and the other contains hydrogen. The pressures of the gas in the two balloons are ___
the same
You are holding two balloons of the same volume. One contains helium, and the other contains hydrogen. The temperatures of the gas in the two balloons are ___
the same
You are holding two balloons of the same volume. One contains helium, and the other contains hydrogen. The numbers of moles of the gas in the two balloons are ___
the same
You are holding two balloons of the same volume. One contains helium, and the other contains hydrogen. The densities of the gas in the two balloons are ___
different
V Ne = 2V Ar
what is the mass ratio of Ne:Ar in the balloons?
1:1
The gas sample is then cooled to a temperature of 15 °C. Solve for the new condition. (Hint: Consider that a moveable piston keeps the pressure constant overall.)
5.43 L
Molar Volume of an Ideal Gas
- For 1 mole of an ideal gas at 0 °C and 1 atm, the volume of the gas is 22.42 L
- STP
standard temperature and pressure (STP)
- 0 °C and 1 atm
- any gas with 0 °C and 1 atm will have a volume of 22.4 L at STP
A sample of oxygen gas has a volume of 2.50 L at STP. How many grams of O2 are present?
3.57 g
Consider the following reaction:
Zn(s) + 2HCl(aq ) -> ZnCl(aq) + H(g)
If 15.00 g of solid zinc reacts with 100.0 mL of 4.00 M hydrochloric acid, what volume of hydrogen gas will be produced at 25 °C and 1.00 atm?
4.89 L
review of liquids and solids
- Gases have low density, are highly compressible, and can fill a container
- solids have high density, are slightly compressible, and are rigid
- Some properties of liquids lie between those of solids and of gases