1. Lesson 65: Take a Breath
Ideal Gas Law

2. ChemCatalyst
Describe how you can determine the volume of a breath of air.
Name four factors that might affect the volume you measure.
What do you need to know in order to determine the number of molecules in a breath of air?

3. Key Question
How can you calculate the number of moles of a gas if you know P, V, and T?

4. You will be able to: define the ideal gas law
define the universal gas constant, R
complete calculations for finding n, using the ideal gas law

5. Prepare for the Lab
Work in groups of four.
Wear safety goggles.

6. Prepare for the Lab (cont.)
The equation for the ideal gas law is
PV = nRT
where R is equivalent to the proportionality constant, k, for this equation.
R = R = L · atm/mol · K
PV nT

7. Discussion Notes
We should see differences in the volume of one breath of air from group to group.
There is more than one way to figure out the volume of air that was exhaled into the bottle.

8. Discussion Notes (cont.)
The ideal gas law allows scientists to relate gas pressure, volume, moles of particles, and temperature.
Ideal Gas Law: The ideal gas law states that PV = nRT, where R, the universal gas constant, is equivalent to the proportionality constant, k, for this equation.
R = R = L · atm/mol · K
PV nT

9. Discussion Notes (cont.)
Note that R is the same for all gases but the value of R does change depending on if the units change.
The number of moles can be converted to the total number of gas molecules by multiplying by 602 sextillion.
The ideal gas law can be used to solve for other variables besides n.

10. Wrap Up
How can you calculate the number of moles of a gas if you know P, V, and T?
The ideal gas law relates volume, pressure, temperature, and the number of moles of a gas sample: PV = nRT, where R = L · atm/mol · K.
R is a number that relates all the different units to one another in the ideal gas law. Its value does not change if the units don’t change. R is called the universal gas constant.

11. Wrap Up (cont.)
The ideal gas law can be used to figure out P, V, n, or T when the other three variables are known.

12. Check-In
You cap a 1.0 L plastic bottle on a mountaintop where the air pressure is 0.50 atm and the temperature is 298 K.
How many moles of gas are in the bottle?
What is the number density, n/V, of the gas inside the bottle on the mountaintop?
At sea level, the volume of the bottle becomes 0.50 L. What is the number density of the gas inside the bottle at sea level?