Chemistry Reference
In-Depth Information
8. A student collects a sample of hydrogen gas, which has a volume of
350 cm
3
at 22.0
o
C. If the pressure of the gas remains constant, what
would be the volume of this gas at standard temperature?
9. A sample of argon gas has a volume of 5.00 L at STP. If the pressure
remains constant, at what temperature would the volume of this gas
reach 10.0 L?
10. A balloon has a volume of 0.855 L at 1.0 atm and 17.0
o
C. If the
pressure remains constant, what will be the volume of this gas at 0
o
C?
Lesson 8-4: Dalton's Law
Dalton's Law of partial pressure states that the total pressure exerted
by a mixture of gases is equal to the sum of each of the partial pressures of
the gases in the mixture. Dalton's Law is expressed by the formula shown
here:
P
total
= P
1
+ P
2
+...P
x
How many “Ps” you show in the formula will depend upon the number
of gases in the mixture. Look at how we use Dalton's Law to solve the
following example.
Example 1
A mixture of gases consists of oxygen, nitrogen, and hydrogen with
pressures of 1.2 atm, 0.8 atm, and 3.5 atm, respectively. Find the
total pressure exerted by this mixture of gases.
P
total
= P
1
+ P
2
+ P
3
= 1.2 atm + 0.8 atm + 3.5 atm = 5.5 atm
* If you are surprised by the way that I rounded in Example 1,
review the rule for addition and subtraction found in Lesson 2-4.
All of the problems using only Dalton's Law will be very easy, but pay
careful attention to the wording. Your teacher may make these problems
slightly harder by making one of the partial pressures the unknown. The
problem is still very easy, but it is possible that you could make a careless
error if you read the question too quickly.
If one of the pressures, say P
2
, is the unknown, simply isolate it on one
side of the equation. Look at Example 2 to see how this is done.
