Chemistry Reference
In-Depth Information
Example 1
A student generates and collects a 550 cm
3
sample of chlorine gas
at 23
o
C and 1.2 atm. What would be the volume of this sample of
gas at STP?
As in the case of working with Charles's Law by itself, we must be sure
to always do our calculations in Kelvin. Therefore, converting to Kelvin, by
adding 273 to the Celsius temperature, is a priority. After that, we can list
the givens, identify the unknown, and solve the equation.
A stu
d
ent generates and collects a 550 cm
3
sample of chlorine gas
at 23
o
C 296 K and 1.2 atm. What would be the volume of this sample
of gas at STP?
Given: V
1
= 550 cm
3
; P
1
= 1.2 atm; T
1
= 296 K,
P
2
= 1.0 atm, T
2
= 273 K
Find:
V
2
V
1
P
1
T
2
P
2
T
1
(550 cm
3
)(1.2 atm)(273 K)
(1.0 atm)(296 K)
V
2
=
=
= 610 cm
3
Formula:
Of course, you might get called on to solve a problem where V
2
is not
the unknown. The key to correctly answering these problems will be your
ability to identify and isolate the unknown. It is an unfortunate fact that
some students do poorly in chemistry, simply because their algebra skills
are somewhat weak. If you identify such a weakness in yourself, don't let it
affect your chemistry class. Get an algebra tutor, or look for Master Math:
Algebra (also published by Career Press).
Let's look at another example.
Example 2
A student collects 4.85 L of hydrogen gas at 314 K and 101.8 kPa of
pressure. The gas is then transferred to a 2.00 L vessel and allowed
to cool to 294 K. What is the new pressure exerted by the gas?
In this example, P
2
is the unknown. In order to isolate P
2
,we must mul-
tiply both sides of the original equation by P
2
and divide both sides by V
2
, as
shown here:
V
2
V
2
V
1
P
1
T
2
P
2
T
1
V
2
P
2
×
=
× P
2
