Gas Laws
Name______________________
Understanding how the temperature, pressure, and density of an air parcel relate
to each other is important to understanding the winds. The ideal gas law for air is
Pressure = 2.87*density*temperature
In this activity you will explore the gas law. The value of 2.87 appears so that
when you use units for density of kg/m3 and Kelvin for temperature, the pressure
units are millibars.
Student Learning Objectives:
Students will:

explore the relationships between pressure, volume, temperature, and density of an ideal gas
(a.k.a. The ideal gas law)

answer specific questions directed at assessing their understanding of these relationships.


use the Gas Law’s virtual environment to accurately collect data.
use a virtual graphing environment to manually graph their data. Assessment of the
agreement between data table and graph will be used to assess student graphing skills.
use graphical analysis of their the data to help answer specific questions related to the
ideal Gas Law.

Part 1 Getting started:
Go to http://phet.colorado.edu/en/simulation/gas-properties and select RunNow
The Youtube video http://www.youtube.com/watch?v=D0zesDZ8r3k introduces
you to the simulation environment.
Start out by putting 20 heavy molecules into the box. Wait about 1 minute for
everything to settle down.
Look closely at the molecules bouncing around.
Does it look like the molecules bounce off the walls with the same speed that
they strike the walls? Yes or NO
Do the molecules bounce off each other? Yes or NO
If Yes, Do the molecules bounce off each other with the same speed that they had
before colliding? Yes or NO
Part 2. Constant Volume.
Clear all molecules from the box by clicking the reset button and then add 100
heavy molecules into the container.
Select the Constant Volume environment.
Vary the temperature from 300 to 900 K by using the heat option. Record the
Pressure and Temperature for at least 6 different temperatures in the 300 to 900
K range. Each time you heat up the gas you must wait for about 20 to 30 seconds
before things settle down. Graph these values on the graph provided. Here’s
another short youtube video with a few tricks related to this activity.
Table 1.
Temperature(K)
Pressure (atm)
Make a graph of pressure on the y-axis vs temperature on the x-axis using the
axes below. See the video Graphing in Word on how to easily plot your data
points on the axes below.
What is the relationship between pressure and temperature at constant volume?
 Using this data, predict at what temperature the pressure will become:
0.20 atm predicted temperature =__________________________
0.1 atm predicted temperature =__________________________
0 atm predicted temperature =__________________________
Remove heat from the chamber to get back to near 300 K with the fixed volume.
The easiest way to do this is click the reset button, select constant volume, and add
100 heavy molecules back into the container. The default setting is that all new
molecules go into the container at a temperature of 300K.
Part 3. Constant Temperature.
Select the Constant Temperature environment.
(make sure you are at 300 K before you switch to constant temperature)
Select Ruler from the measurement tools and use it to measure the volume of the
gas in relative units.
In the image below the ruler is measuring the volume to be 6.6 relative units.
Vary the volume by sliding the left wall to the right or left and record at least 6
different Volume Pressure pairs. Each time change the volume you must wait for
about 20 to 30 seconds before things settle down. Record the Volume Pressure
pairs in the table below and then graph these values on the graph provided.
Table 2.
Volume
(relative units)
Pressure (atm)
Make a graph of pressure on the y-axis vs relative volume on the x-axis using the
axes below. See the video Graphing in Word on how to easily plot your data
points on the axes below.
What is the relationship between pressure and Volume at constant Temperature?
 Using this data, predict at what Volume the pressure will become:
3.00 atm predicted volume =__________________________
0.1 atm predicted volume =__________________________
Although the temperature readjusts to 300 K when constant temperature is
selected, the temperature does change a bit when the volume changes.
Does the temperature increase or decrease when the volume increases?
Does the temperature increase or decrease when the volume decreases?
The density is the mass or number of molecules per unit volume
Relative Denisty 
Number of molecules
Relative Volume
Using 100 for the Number of molecules calculate the relative density for the
volumes in Table 2. Record these values in Table 3 below and then graph these
values on the graph provided. Here’s an online calculator for easy use.
Table 3.
Relative Density
Pressure (atm)
Make a graph of pressure on the y-axis vs relative density on the x-axis using the
axes below. See the video Graphing in Word on how to easily plot your data
points on the axes below.
 What is the relationship between pressure and Density at constant Temperature?
Part 4. Constant Pressure
Reset the number of molecules to 100 and keep the constant temperature setting
selected until the temperature settles back to 300 K for a relative volume around
6.6.
Now select constant Pressure
Using the heat control to add or remove
heat vary the temperature from 150 K to
350 K and for each temperature measure
the new volume (with the ruler tool) after
everything has settled down. Record these
Temperature and Volume pairs in Table 5
below and then graph these values on the
graph provided (Graph 4)
Table 4.
Temperature(K)
Volume
(Relative Units)
Make a graph of Volume on the y-axis vs Temperature on the x-axis using the axes
below. See the video Graphing in Word on how to easily plot your data points on
the axes below.
 What is the relationship between Volume and Temperature at constant Pressure?
 Using this data, predict at what Temperature the volume will become :
10 Volume units predicted temperature =__________________________
1.0 Volume units
predicted temperature =__________________________
When a parcel of air is heated up near the surface it expands but its pressure stays
constant because the weight of air from above stays the same. As the temperature
of the parcel increases the density becomes _______________ [lower or higher]
and the air parcel ______________ [rises or sinks].