http://www.ck12.org Chapter 14. The Behavior of Gases
Lesson Summary
- According to Dalton’s law, the sum of the individual partial pressures of the gases in a mixture is equal to the
total gas pressure. - The partial pressure of a gas in a mixture can be calculated by multiplying its mole fraction by the total
pressure. - The pressure of a gas that has been collected by water displacement is determined by subtracting the vapor
pressure of water at that temperature from the total pressure of the sample. - Diffusion is the net movement of molecules from an area of high concentration to an area of lower concen-
tration. Effusion is the process of a gas escaping from a tiny hole in its container. Graham’s Law allows the
relative rates of diffusion or effusion for various gases to be calculated from the molar masses of the gases.
Lighter gases move at a faster rate than heavier gases, resulting in faster diffusion and effusion rates.
Lesson Review Questions
Reviewing Concepts
- Explain what is meant by the term partial pressure.
- What is a mole fraction? What must be the sum of the mole fractions for all substances in a mixture?
- Why does a gas displace water when bubbled into it?
Problems
- Hydrogen, nitrogen, and oxygen gases are mixed into a container with a total pressure of 767 mmHg. If the
partial pressure of the hydrogen is 85 mmHg, and the partial pressure of the nitrogen is 517 mmHg, what is
the partial pressure of the oxygen? - On the summit of Mount McKinley, the highest mountain in North America, the atmospheric pressure on a
certain day is about 338 mmHg. Given that the mole fraction of oxygen in Earth’s atmosphere is 0.2095, what
is the partial pressure of oxygen on the summit of Mount McKinley? - Rank the following gases by their average velocities at a given temperature, from slowest to fastest: Ar, SO 2 ,
N 2 , CH 4 , Kr. - A mixture is made of 32.5 g of helium gas and 38.7 g of neon gas.
a. Calculate the mole fraction of each of the two gases.
b. The total pressure in the container is 278 kPa. Calculate the partial pressure of each gas.- 2.20 liters of gas is collected over water at a temperature of 30°C and a total pressure of 98.05 kPa. Find the
volume that the dry form of this gas would occupy at STP. - What is the ratio of the effusion rates for oxygen gas and xenon gas when both gases are at the same
temperature and pressure? - At a certain temperature and pressure, the average velocity of N 2 molecules is 524 m/s. What is the average
velocity of O 2 molecules at the same temperature and pressure? - Water can be made to decompose into hydrogen and oxygen gases by passing an electrical current through it.
2H 2 O(l)→2H 2 (g) +O 2 (g)A 50.0 g sample of water completely decomposes in a sealed 10.0 L container
that was previously under vacuum. The temperature is 25°C. Determine the partial pressure (in atm) of both
gases produced in the reaction.