http://www.ck12.org Chapter 14. The Behavior of Gases
Note that the final number of moles has to be calculated by adding the original number of moles to the moles of
added helium. Use Avogadro’s Law to solve for the final volume.
Step 2: Solve.
First, rearrange the equation algebraically to solve for V 2.
V 2 =
V 1 ×n 2
n 1Now, substitute the known quantities into the equation and solve.
V 2 =
1 .90 L× 0 .1130 mol
0 .0920 mol= 2 .33 L
Step 3: Think about your result.
Since a relatively small amount of additional helium was added to the balloon, its volume increases slightly.
Practice Problem- 2.50 g of CO 2 gas is confined in a rigid cylinder at a pressure of 4.65 atm. If 0.42 g of gas is released from the
cylinder, what is the new pressure?
Watch a simulation of Avagadro’s Law at http://www.dlt.ncssm.edu/core/Chapter7-Gas_Laws/Chapter7-Animati
ons/Avogadro%27sLaw.html.
Lesson Summary
- As the pressure of a gas increases, its volume decreases if the temperature is held constant.
- As the absolute temperature of a gas increases, its volume also increases if the pressure is held constant.
- As the absolute temperature of a gas increases, its pressure also increases if the volume is held constant.
- The combined gas law is used when the pressure, volume, and temperature of a gas all change.
- As the number of moles of gas increases, its volume increases if the pressure and temperature are held constant.
Lesson Review Questions
Reviewing Concepts
- Why is it necessary to use Kelvin temperatures in all gas law calculations that involve temperature?
- Explain the difference between a direct and an inverse relationship.
Problems
- 2.20 L of air at 1.10 atm is allowed to expand to fill a 6.30 L container. Find the final pressure.
- A balloon is inflated to a volume of 1.25 L. If the temperature of the air inside is cooled from 35°C to 15°C,
what will be the final volume of the balloon?