Chemistry Reference
In-Depth Information
Boyle's Law can be used to solve for an unknown volume or pressure,
when the temperature and the number of particles in the sample remain
constant. Let's try a few examples.
Example 1
A sample of neon gas has a volume of 250 cm
3
and a pressure of
86.7 kPa. At what volume would this gas exert 100. kPa of pressure?
(Assume the temperature remains constant.)
We will start by listing what we have been given and identifying the
unknown, which is Volume 2 (V
2
). We will then take the original formula
for Boyle's Law and isolate the unknown by dividing both sides by P
2
. After
dividing both sides of the equation by P
2
to isolate V
2
, we get our working
formula. We then substitute and solve, as shown here:
Given: V
1
= 250 cm
3
; P
1
= 86.7 kPa; P
2
= 100. kPa
Find:
V
2
P
1
V
1
P
2
(86.7 kPa)(250 cm
3
)
(100. kPa)
Formula:
V
2
=
=
= 216.75 cm
3
Answer rounded is 220 cm
3
Now, I will show an example where the second pressure is the unknown.
I will do all of the work in one step, but if I lose you, you can refer back to
Example 1 to see what I did.
Example 2
A student collects 435 cm
3
of hydrogen gas at 2.3 atm of pressure.
Assuming the temperature of the gas doesn't change, at what
pressure would this gas occupy 500. cm
3
?
Given: V
1
= 435 cm
3
; P
1
= 2.3 atm; V
2
= 500. cm
3
Find:
P
2
P
1
V
1
V
2
(2.3 atm)(435 cm
3
)
(500. cm
3
)
Formula:
P
2
=
=
= 2.001 atm
Answer rounded is 2.0 atm
Eventually you will find that you can solve many of the easiest examples
of Boyle's Law calculations in your head, just by understanding what it means
to say that the pressure and volume of the gas are inversely proportional.
Look at Example 3 as an illustration of what I mean.
