Chemistry Reference
In-Depth Information
7.
A sample of chlorine gas is collected in a bottle by displacing water at
a temperature of 20.0
o
C. The total pressure exerted by the mixture
of chlorine and water vapor is 85.6 kPa. What is the pressure of the
dry chlorine gas?
a) 85.6 kPa
b) 2.34 kPa
c) 83.3 kPa
d) 87.94 kPa
8.
A mixture of gases is composed of 1.00 mole of carbon dioxide, 2.00
moles of helium, and 2.00 moles of oxygen. If the total pressure is
1.00 atm, what is the partial pressure of the carbon dioxide?
a) 0.100 atm
b) 0.200 atm
c) 0.400 atm
d) 1.00 atm
Lesson 8-5: Combined Gas Law
Although you learn about each of these gas laws in isolation, in reality,
you often will need to use some combination of them in experimental situ-
ations. The term Combined Gas Law could really refer to any combination
of gas laws, which you find yourself using. Often, however, the term is used
to describe the combination of Boyle's Law and Charles's Law, which is
often used to mathematically adjust the volume of a gas to STP conditions.
You see, it is unlikely that a student or scientist will actually be measur-
ing the volume of a gas at standard temperature and pressure. Standard
temperature is 0
o
C, and that is colder than most of us would want to work
at. Variations in temperature and pressure result in significant changes in
the volume of a gas, and it is difficult to visualize the quantity of a gas at
varying conditions. It is very common for this reason to mathematically
determine the volume that a gas sample would occupy at STP. In order to
do this, we combine Charles's and Boyle's Laws into the formula shown
here.
The Combined Gas Law
V
1
P
1
T
2
P
2
T
1
V
2
=
Keep in mind that the subscript numbers (as in V
1
and V
2
) don't refer
to the order in which the quantities appear in the word problem; rather,
they refer to “before” and “after,” or “initial” and “final.” Let's go over an
example of how this formula is used.
