14.2. Gas Laws http://www.ck12.org
When a certain sample of oxygen gas is placed in a 425 mL container, its pressure is equal to 387 kPa. The gas is
allowed to expand into a 1.75 L container. Calculate the new pressure of the gas.
Step 1: List the known quantities and plan the problem.
Known
- P 1 = 387 kPa
- V 1 = 425 mL
- V 2 = 1.75 L = 1750 mL
Unknown
- P 2 =? kPa
Use Boyle’s Law to solve for the unknown pressure (P 2 ). It is important that the two volumes (V 1 and V 2 ) are
expressed in the same units, so V 2 has been converted to mL.
Step 2: Solve.
First, rearrange the equation algebraically to solve for P 2.
P 2 =
P 1 ×V 1
27.22 V
Now, substitute the known quantities into the equation and solve.
P 2 =
387 kPa×425 mL
1750 mL
= 94 .0 kPaStep 3: Think about your result.
The volume has increased to slightly over four times its original value, so the pressure is decreased approximately
fourfold. The pressure is in kPa, and the correctly rounded value has three significant figures.
Practice Problem- What is the new volume of a sample of neon if 5.23 L of the gas, which was originally at 214 mmHg, is
compressed until the pressure increases to 796 mmHg? - When a balloon containing 635 mL of air is taken from sea level (at standard pressure) to a higher altitude, the
balloon expands to 829 mL. What is the air pressure at this new altitude (in atm)?
If you need more information on Boyle’s Law, NASA explains it at http://www.grc.nasa.gov/WWW/k-12/airplan
e/boyle.html.
You can watch an animation of Boyle’s Law at http://www.dlt.ncssm.edu/core/Chapter7-Gas_Laws/Chapter7-Ani
mations/BoylesLaw.html.
Boyle’s Law has an interesting application—the potato gun. As the volume of air decreases in a PVC pipe, pressure
builds and causes a potato plug to launch. Watch this at http://www.youtube.com/watch?v=OolForRzsRk.
A Boyle’s Law lab can be viewed at http://www.youtube.com/watch?v=LVE4PUHqPjk&feature=player_embedded
. The document that accompanies this lab is found at http://www.dlt.ncssm.edu/core/Chapter7-Gas_Laws/Chapter7
-Labs/Boyle%27s_Law_CBL_web_01-02.doc.
Boyle’s Law demonstrations can be seen at http://www.youtube.com/watch?v=N5xft2fIqQU.