http://www.ck12.org Chapter 14. The Behavior of Gases
Watch a simulation of Gay-Lussac’s Law at http://www.dlt.ncssm.edu/core/Chapter7-Gas_Laws/Chapter7-Animati
ons/Gay-Lussac%27sLaw.html.
A video of a Gay-Lussac’s Law lab is at http://www.youtube.com/watch?v=1pVVZGOBIVg&feature=player_em
bedded. The accompanying document for this lab is found at http://www.dlt.ncssm.edu/core/Chapter7-Gas_Laws/
Chapter7-Labs/Gay_Lussac’s_Law_web_01-02.doc.
Learn more about Gay-Lussac’s Law and Charles’s Law at http://www.grc.nasa.gov/WWW/k-12/airplane/glussac.ht
ml.
The Combined Gas Law
To this point, we have examined the relationships between any two of the variables P, V, and T, while the third
variable is held constant. However, situations can also arise where all three variables change. Thecombined gas
lawexpresses the relationship between the pressure, volume, and absolute temperature of a fixed amount of gas. For
a combined gas law problem, only the amount of gas is held constant.
P×V
T=k andP 1 ×V 1
T 1
=
P 2 ×V 2
T 2
Sample Problem 14.4: Combined Gas Law
2.00 L of a gas at 35°C and 0.833 atm is brought to standard temperature and pressure (STP). What will be the new
gas volume?
Step 1: List the known quantities and plan the problem.
Known
- P 1 = 0.833 atm
- V 1 = 2.00 L
- T 1 = 35°C = 308 K
- P 2 = 1.00 atm
- T 2 = 0°C = 273 K
Unknown
• V 2 =? L
Use the combined gas law to solve for the unknown volume (V 2 ). STP is 273 K and 1 atm. The temperatures have
been converted to Kelvin.
Step 2: Solve.
First, rearrange the equation algebraically to solve for V 2.
V 2 =
P 1 ×V 1 ×T 2
P 2 ×T 1
Now substitute the known quantities into the equation and solve.
V 2 =
0 .833 atm× 2 .00 L×273 K
1 .00 atm×308 K