Little Guys In Motion
Gases are made up of many little molecules that are constantly in motion. When these little guys bounce around off of the walls of a container, they exert pressure. This is a simplified version of the kinetic molecular theory! The hotter the temperature, the faster the molecules go and the more they collide. This means that temperature and pressure is a direct relationship, which is Amonton’s gas law! We did an experiment to test this law. Here is the procedure:
1. Prepare four 600 mL beakers of about 400 mL water each. One of boiling water, one of hot tap water, one of room temperature water, and a last of ice water.
2. Prepare a Temperature Probe and Gas Pressure Sensor for data collection as well as a computer program for data collection.
3. Collect pressure vs. temperature data for your gas sample.
a. Place the flask into the ice-water bath. Make sure the entire flask is covered.
b. Place the temperature probe into the ice-water bath and when the pressure and temperature readings displayed in the meter stabilize, collect and save the data.
4. Repeat Step-3 procedure using the room-temperature bath, hot water, and boiling water bath.
Check out a few pictures of the process!
To determine a direct relationship, we needed to calculate a proportionally constant, k, from our data. Is our constant, k, the same when dividing the temperature (must be in Kelvin) by the pressure? Take a look!
If you thought k was pretty constant from our data, you’re right! Our values were constant because the range was from 0.266 to 0.272. The equation to express the relationship between pressure and temperature is k=pt. Based on our data from the lab and also the equation that expresses the relationship between pressure and temperature, do you think if the temperature is doubled, the pressure of a gas should also be doubled? Let’s think about this mathematically. If our equation is k=p/t, then p1/t1=k and p2/t2=k should equal the same constant, meaning p1/t1=p2/t2 are equal to each other. For example, the equation 1/200=2/400 is equal because 2/400 is just 1/200 doubled.
Our experiment proved that Amonton’s gas law is correct! The relationship between gas pressure and temperature is when the temperature rises, the pressure rises. This is because heat makes the gas molecules move faster so they collide more and it creates more pressure. If the temperature lowers enough, the gas molecules will stop moving and exert no pressure. This is called “absolute zero”. For another experiment on Amonton’s gas law and the kinetic molecular theory, follow the link to find a MythBusters’ video where they test if your water heater can build up enough pressure for it to blast through the roof of your house!
Can you think of other ways to test Amonton's gas law and the kinetic molecular theory? Let us know in the comments below!