Download UNIT 9 – GASES

GASES
KINETIC MOLECULAR THEORY (KMT) (pp. 426-429)
1. The kinetic molecular theory was developed to help predict the behavior of gases. It describes the
behavior of gases at the molecular level.
2. This theory is based on assumptions about a theoretical gas known as an ____________________.
3. The assumptions are:
a. Ideal gas particles are so small that the volume of the individual particles if they were at rest is
essentially zero when compared with the total volume of the gas.
b. Ideal gas particles are in constant, rapid, random motion, moving in straight lines in all directions until
they collide with other particles.
c. There are no attractive or repulsive forces between particles and collisions between particles are elastic.
d. The average kinetic energy of the particles is directly proportional to the absolute temperature (measured
in Kelvins).
FOUR VARIABLES DESCRIBE A GAS
Temperature
1. The temperature of a gas determines the average kinetic energy of the particles.
2. While the average kinetic energy of a collection of gases at a given temperature will be same, the
velocity at which they travel will not. This is because the mass values of the various gases are different.
3. Temperature is usually measured in either Celsius or Kelvin. Both are related to one another:
Volume
1. A derived unit:
2. Gas volumes are expressed four different ways:
Pressure
1. The force that the gas particles exert over a unit area:
2. Pressure is a measure of the total force exerted by the moving particles of a gas as they collide with the
walls of the container.
3. Atmospheric pressure is measured in terms of:
Standard Temperature and Pressure (STP)
1. In order to study the effects of changing temperature and pressure on a gas, one must have a standard for
comparison.
2. STP represents a pressure and temperature that are fairly easy to reproduce:
Particles
1. Gases with equal volumes under the same conditions of pressure and temperature have equal numbers of
particles.
2. This is ______________________________ and it holds true only for gases.
3. The amount of gas is measured in __________.
4. The volume of one mole of gas at STP is known as the _________________________.
GAS LAWS (pp. 403-415)
1. The gas laws are a series of mathematical relationships that relate the following variables:
Charles’ Law
1. Relates volume and temperature.
2. As the temperature decreases, the volume of a gas decreases. As temperature increases, the volume of a
gas increases.
3. The volume of a gas at constant pressure is directly proportional to the absolute temperature.
4. Charles’ Law helped prove the existence of absolute zero.
5. Mathematically this is:
6. If the volume divided by the temperature is a constant, we can equate this ratio for gases under two sets
of conditions:
Therefore:
***** A sample of gas occupies 24.0m3 at 100.0K. Determine its volume at 400.0K.
***** Gas in a balloon occupies 2.50L at 300.0K. At what temperature will the balloon expand to 7.50L?
Boyle’s Law
1. The volume of a gas at constant temperature is inversely proportional to the pressure.
2. Like Charles’ Law, we can write:
***** The gas in a balloon has a volume of 4.00L at 100.0kPa. The balloon is released into the atmosphere
and the gas in it expands to a volume of 8.00L. Determine the pressure on the balloon at the new volume.
***** If the pressure of a 2.50m3 sample of gas is 1.50 atm, what volume will the gas occupy if the
pressure is changed to 7.50 atm?
Gay-Lussac’s Law
1. The pressure of a given gas varies with the Kelvin temperature when the volume remains constant.
2. This is expressed as:
***** The pressure of a gas in a tank is 324.24kPa at 295.0K. Determine the gas pressure if the
temperature is raised to 333.0K.
***** A gas in a sealed container has a pressure of 125.0kPa at 30.0 0C. Determine the temperature in the
container if the pressure is increased to 201.0kPa.
Dalton’s Law (pp. 420 – 425)
1. The total pressure in a gas mixture is the sum of the partial pressures of the individual components.
2. The _________________________ of a gas is the pressure of an individual gas in a gas mixture that
contributes to the total pressure of the mixture.
3. This is expressed mathematically as:
4. Dalton’s law is often used to determine the pressure of a gas collected over water.
***** Hydrogen gas is collected over water at a total pressure of 95.0kPa. The volume of gas collected is
28.0mL at 25.00C. Determine the partial pressure of the hydrogen gas if the water vapor pressure is
3.17kPa.
***** A gas is collected over water at 50.00C and a barometric pressure of 105.00kPa. Determine the
pressure of the gas if the water vapor pressure is 12.34kPa.
COMBINED GAS LAW
1. The combined gas law states the relationship among pressure, volume and temperature of a fixed
amount of gas:
2. The combined gas law allows one to work out problems involving more variables that change.
***** A gas at 110.0kPa and 30.00C fills a flexible container with an initial volume of 2.00L. If the
temperature is raised to 80.00C and the pressure increased to 440.0kPa, what is the new volume?
***** At 0.000C and 1.00 atm pressure, a sample of gas occupies 30.0mL. If the temperature is increased
to 30.00C and the entire gas sample is transferred to a 20.0mL container, what will be the gas pressure
inside the container?
IDEAL GAS LAW (pp. 415-420)
1. The number of moles is the fourth variable that can be used along with pressure, volume and
temperature to describe a gas.
2. The ideal gas law is:
3. If pressure is expressed in atmospheres, then:
4. If pressure is expressed in kPa, then:
***** Determine the number of moles of gas in a 3.00L container at 300.0K and a pressure of 1.50 atm.
***** Determine the Celsius temperature of 2.49 moles of gas contained in a 1.00L container at a pressure
of 143kPa.
GAS STOICHIOMETRY (pp. 430-434)
1. The coefficients in a chemical equation represent molar amounts of substances taking part in a reaction.
2. Avogadro’s principle states that equal volumes of gases at the same temperature and pressure contain
equal numbers of particles. Thus, when gases are involved, the coefficients in a balanced equation also
represent volumes.
***** Determine the volume of oxygen gas needed for the complete combustion of 4.00L of propane gas
(C3H8). Assume constant pressure and temperature.
C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)
***** Ammonia gas is synthesized from hydrogen gas and nitrogen gas:
N2(g) + 3H2(g) →2NH3(g)
If 5.00L of nitrogen reacts completely with the hydrogen at a pressure of 3.00 atm and a temperature of
298K, how many grams of ammonia are produced?
***** When iron rusts, it undergoes a reaction with oxygen to form iron (III) oxide:
4 Fe (s) + 3 O2 (g) → 2 Fe2O3 (s)
Determine the volume of oxygen gas at STP that is required to completely react with 52.0 g of iron.