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Atmosphere and Gas Laws

Posted: Thu Dec 13, 2007 5:38 pm
by bclaw2011
For my science experiment, I am trying to determine if either pressure or temperature has the greatest effect on the amount of air in the atmosphere. I am proposing to determine this using Boyle's Law and Charles' Law. At the moment I am still trying to find out how I am going to use my results form the laws and relate it to the atmosphere.
In my experiemntal design, a syringe will be used to trap air. For Boyle's Law, the air in the syringe will be heated in a pot of water which is expected the amount of air in the sealed syringe. For Charles' Law, the same syringe will be placed in the holes of two wooden blocks. 1 kilogram bricks will be on top one at a time affecting theamount of air in the syringe. So my question is this:
Is it too irrevelant to come up with a result about the atmosphere using the data collected form the gas law experiments?
Also, which factor can I use to find the effect since effects cannot be measured?

Posted: Thu Dec 13, 2007 6:17 pm
by Craig_Bridge
I am trying to determine if either pressure or temperature has the greatest effect on the amount of air in the atmosphere.

This isn't stated as a hypothesis that can easily be tested. This sentence leaves open the question of whether something else (besides pressure and temperature) have a bigger effect on the amount of air in the atmosphere.

I'm sure you can come up with an interesting hypothesis that can be tested that is related; however, it is going to be hard to do something on a small scale and extrapolate that to the entire atmosphere.

What grade are you in? I'm going to assume that you've had some algebra based on your choice of projects and are at least in middle school. Have you had chemistry?

If you think about the atmosphere of the earth as a closed system (assumes that gas in the atmosphere doesn't float away into space), then if nothing was changing gas into liquid or solid or vice versa, then the amount of air in the atmosphere in terms of number of atoms would be constant.

Posted: Fri Dec 14, 2007 6:24 am
by bclaw2011
Thank you for your reply Craig. I am a high school sophmore currently taking chemistry. So are you saying that I should use another factor to state a suitable hypothesis :?: My hypothesis is as both pressure and temperature increases the surface will increase. So I already know I will most likely have to a certain effect that can be measured. I also know that the atmosphere cannot be considered as a closed system beacuse it is, so can you help me on what to do next :?:

Posted: Fri Dec 14, 2007 9:37 am
by Craig_Bridge
My hypothesis is as both pressure and temperature increases the surface will increase.
If we simplify to an ideal gas that doesn't undergo phase changes, PV = nRT.

I don't see a "surface" involved anywhere unless you make it the surface area of the volume that contains the gas. If we assume a sphere, then surface area will increase with volume. If the number of moles of the gas remain the same, the equation predicts
1) presure going up and temperature constant means volume decreases (inverse relationship), and
2) Temperature going up and pressure constant means volume increases (normal relationship)

Your hypothesis has both an inverse and normal relationship so there is going to be some cancellation of effects.

Are you more interested in the atmosphere (macro level) or are you more interested in things that can be done in the lab (micro level).

If you are more interested in things that can be done in a lab, then that opens areas of investigation to state changes and thermodynamics.

Micro Level

Posted: Fri Dec 14, 2007 4:53 pm
by bclaw2011
Ok Craig. I do want to do things in a lab but I thought I was gonna get more project depth if I related it to the atmosphere. But if I were to do things on a macro level, could you tell me what would happen :?:

Posted: Fri Dec 14, 2007 5:01 pm
by bclaw2011
Also Craig I was actually referring to the surface being the surface area around a particular object, specifically around the outer layer of the atmosphere.

Posted: Fri Dec 14, 2007 5:55 pm
by bclaw2011
Sorry, but I also found something new. I think that if I use the mass of the atmosphere, which is 5E18 kilograms according to the following site: (E= 10 to the exponent in this case eighteen) 8) . Using this same number I can find the number of molecules in the atmosphere. Using the same number I will divide the number by 35 and state my results asthat. But, I just thought of something else. How about I use the results from the experiment and use my conclusions to the realte to the atmosphere :!: :!:

Posted: Mon Dec 17, 2007 3:45 pm
by bradleyshanrock-solberg
Take what I'm saying with a grain of salt because it's been about 20 years since I had a course on planetary-level heavenly bodies and the geophysics of them, but you're having trouble because what you're trying to compare isn't very similar.

At the planetary scale, atmosphere is held on pretty much by gravitational effects, and ground level air pressure is just the weight of the atmosphere above wherever you're standing.

Temperatures affect the composition of the atmosphere more than the pressure...some elements freeze out or boil into the atmosphere that are different if the same planet is located where Mars is, vs where we are or where Venus is. Indeed, Venus and Earth are pretty similar with respect to gravitational force, but Venus has very different atmosphere. Some of that is the heat, some is differences in the planet itself (atmosphere being the part of the planet that is in gaseous phase, rather than solid).

Human scale temperature changes cause weather, not radical changes in shape or composition of atmosphere. You might have better luck comparing your experiments to low/high presssure systems that affect storm formation. Hot temperatures at sea level, often the seawater itself colliding with cold temperature air higher up can cause "hot air rises" effects that eventually mutate into something as dramatic as a hurricane.

Again though, these pressure changes are unconstrained. The gas moves where it wants to go, and it's measurable at sea level with changes in barometric pressure that predict weather changes. I don't understand this topic well enough though to find a correlation to laboratory Boyles's law and Clark's law experiements.

Posted: Wed Dec 19, 2007 4:47 pm
by bclaw2011
But is it possible to convert the results I receive from the Boyle's Law and Charles's Law and apply it to the atmosphere

These two projects at these sites were combined: ... ?from=Home ... p011.shtml
Please view these before resopnding. :D
If not, can anyone help me come up with how the use of Boyle's Law and Charles's Law effects the world besides the atmosphere :?:

Posted: Wed Dec 19, 2007 5:36 pm
by bradleyshanrock-solberg
To the atmosphere as a whole (all over the planet), no.

Temperature isn't constant (equatorial atmosphere is warmer than polar atmosphere), and pressure isn't constant as well.

It's a continuum, with temperature getting colder and pressure decreasing as the atmosphere becomes thinner, modified by small scale pressure and temperature effects that we think of as weather. The overall volume of the Earth's atmosphere is a function of the planet's gravity and its composition, mostly. There is a gravity element missing from the two experiments you reference. Instead of measuring the pressure exerted by a volume of air in a fixed space at varying temperature (for example) you have an entirely open space that in absence of gravity would disperse the atmosphere entirely.

You might be able to somehow connect ambient temperature to the air pressure at a given altitude. But I can't see how to fit volume into the mix.

I wish I could come up with something clever here, but I think the atmosphere's attraction to Earth and its volume is fundimentally different from the experimental setup in these experiments.

I've Come To My Senses

Posted: Wed Dec 19, 2007 5:38 pm
by bclaw2011
After doing more research, I understand that the results that I will recieve from the experiment will not be able to be used to draw conclusions about the atmosphere and it be accurate. This is because I have just realized that there are no constant variables of temperature, volume, or pressure in the atmosphere due to it (the atmosphere) not being a closed system. So how do I draw a conclusion for my project? That is the about the only problem I have now. :) Please refer to the websites in the previous message if you have the need for my project information in order to help me with figuring this out. Thank you. :D

Posted: Wed Dec 19, 2007 5:47 pm
by bradleyshanrock-solberg
All I can think of is for you to be applying this to some real world, small scale phenomina that's more similar to your pressure jars etc, from the experiments.

For example...consider the air inside an airplane. That's a pressurized, temperature controlled environment. So is a submarine, or a compressed air cannister (scuba gear). To some extent a weatherproof house is too.

You might be able to relate what you learned from the experiment to real life somehow (eg, it might be a bad idea to let a SCUBA air tank get too hot, or the heat generated by passengers in an airplane might cause air pressure to increase).

A lot of people do worry about pressure exerted by gasses, so if you can relate a change in pressure to a change in temperature there could be a hook you can use to make what you've done more relevant or interesting.