Gases ❮ 119attain equal kinetic energy. For this reason, the
speeds are not identical.- C—The smaller the gas particle and the less
polar (more nonpolar) the gas is, the smaller
the deviation from ideal gas behavior. Sulfur
dioxide, SO 2 , is the only polar gas; therefore, it
will most likely show the greatest deviation. The
remaining species (nonpolar) should be in order
of increasing molar mass. - D—This behavior is due to kinetic molecular
theory. The average kinetic energy depends only
on the absolute temperature. The average speed
changes with the atomic mass, with the heavier
gas moving more slowly. Since the volumes are
all the same, the higher the atomic mass, the
higher the density.- A—All three variables will change, which makes
this the best answer. The escaping gas would
lead to a decrease in the number of moles.
If there are fewer moles present, the pressure
would decrease. The slower-moving gas mol-
ecules would tend to remain in the container,
while the faster-moving molecules would escape.
This would result in a lower average velocity of
those species remaining in the container. If there
is a lower average velocity, then there will be a
lower temperature.
❯ Free-Response Question
You have 20 minutes to answer the following question. You may use a calculator and the
tables in the back of the book.Question
A sample containing 2/3 mol of potassium chlorate, KClO 3 , is heated until it decomposes
to potassium chloride, KCl, and oxygen gas, O 2. The oxygen is collected in an inverted
bottle through the displacement of water. Answer the following questions using this
information.
(a) Write a balanced chemical equation for the reaction.
(b) Calculate the number of moles of oxygen gas produced.
(c) The temperature and pressure of the sample are adjusted to STP. The volume of the
sample is slightly greater than 22.4 L. Explain.
(d) An excess of sulfur, S, is burned in one mole of oxygen, in the presence of a catalyst, to
form gaseous sulfur trioxide, SO 3. Write a balanced chemical equation, and calculate
the number of moles of gas formed.
(e) After the sulfur had completely reacted, a sample of the residual water was removed
from the bottle and found to be acidic. Explain with a balanced chemical equation.❯ Answer and Explanation
(a) 2 KClO 3 (s) → 2 KCl(s) + 3 O 2 (g)
You get 1 point if you have the correct set-up of reactant and products. You get
1 more point if the equation is balanced correctly.
(b) (2/3 mol KClO 3 ) (3 mol O 2 /2 mol KClO 3 ) = 1 mol O 2
You get 1 point for the correct answer and 1 point for the work. You can get these
points if you correctly use information from an incorrect equation in part a.