Combined Gas Law Experiment

[ScienceGeek]

Hi, for my high school project we have to present a demo showing the combined gas law. I've looked all over the internet and have tried to come up with some ideas, but I cannot think of anything. We need something that will show the basic theory, without having to provide any measurements or anything.

 

Thank you for your time ;D

[DJBruce]

Since this is homework I first have to ask you; what is the combined gas law? What does each relationship mean?

 

What might happen if you place a sealed balloon inside a Dewar of liquid nitrogen? What if you carefully heated the balloon? What causes these changes?

 

If you answer those questions you will probably be able to figure out a fairly easy demonstration. If you want more help post some of your thoughts on the topic, or on my questions, and I'll be more than happy to help. However, it is forum policy not to directly due homework for other members.

[ScienceGeek]

The combined gas law relates temperature, volume, and pressure. But by placing a balloon in a dewar of liquid nitrogen, that's only cooling it. By heating a ballon, that's heating it. Those affect temperature but not pressure. So I think we need to incorporate pressure, but I see no way of doing that in a classroom. Is there any apparatus I may have never heard about that can do such thing?

 

&thank you for your help !!

[DJBruce]

You are right that you are varying the temperature of gas, however, do not forget Gay-Lussac's Law. According to it [math]T \propto P[/math]. So by varying the temperature of the gas you will actually cause a change in pressure. This can be explained according to the kinetic-molecular theory of gases, but I will leave it up to you to figure that out. When you cool the balloon you see that the balloon shrinks, it decreases in volume. This decrease in volume is caused by a reduction in pressure inside the balloon meaning the pressure outside the balloon is greater than it is inside.

 

If you wish to use a different demonstration to show Boyle's Law you could simply place a barometer and a balloon inside a vacuum chamber. As the vacuum evacuate the chamber the barometer will show a drop in pressure. As the pressure drops the balloon will begin to expand according to Boyle's Law. A vacuum chamber is a fairly standard piece of lab equipment, and your school more than likely has one.

[ScienceGeek]

Ah thank you so much!

[hermanntrude]

Boyle's law is easy to demonstrate using a J-tube (google it). You don't have to use mercury, either, water will work fine. an important thing is that the tube should be quite wide, though.