<p>I'm preparing for the Chemistry SAT2 and so my teacher from last year gave me some tests to refresh my memory on it. My physics teacher from this year is actually including it in my grade since the two are good friends and have talked about it. Anyways I took a test after school today and this was the questiom: </p>
<p>Argon gas is present in a container at 50 degrees Celsius and is cooled to 25 degrees celsius. If the vloume stays constant, which of these will also decrease?:</p>
<p>I) molar mass of the molecules
II) average distance between the gas particles
III) pressure the gas exerts on the container</p>
<p>a) I only
b) I and II only
c) I and III only
d) II and III only
e) III only</p>
<p>I put D but I'm not sure. Any chem whiz's here?</p>
<p>The molar mass of particles depends on chemical composition. Unless the particles react to form new products, that property will not change.</p>
<p>The average distance between gas particles will decrease because their average kinetic energy will decrease, causing less rigorous motion and allowing more time for intermolecular forces to act.</p>
<p>The pressure of the gas is directly proportional to its temperature. PV = nrT</p>
<p>I thought it's D, definitely no for i), and yes for iii). But...
Actually, it was on my AP chem class mid-term and my teacher said average distance is nothing to do with temperature.
Since the volume stays constant, it would be same, that's what she said.
Now I am confused. What's the answer?</p>
<p>D is correct on a very technical level. However, teachers may say (like in my case) that the intermolecular forces are so weak even at 25 degrees Celcius that the effect is negligible.</p>
<p>It could be E in that :
1) Since the volume of the container stays constant, the gas will be diffused throughout a large area.
2) The gas particles are moving at a slower rate.</p>
<p>1 & 2 combined, the particles collide less frequently at a close enough distance for intermolecular forces to work.</p>
<p>well ok, it seems that either answer could be up for legit debate. This is what I'll do: If the answer is D, swell, if it's E, then I'll argue my case by saying what goirulz said. Originally when takng the test I read through it and forgot that the volume remained constant, so I thought of course D. But now this kinetic energy business is becoming appealing to me.</p>
<p>This is why it's important to understand what point masses and ideal gases are. One of the fundamental assumptions is that there are no intermolecular forces in an ideal gas. Don't assume that it isn't a real gas just because they give you an example (argon). Instead, assume it's an ideal gas. Therefore, you have to accept that the particles will take up the entire volume of its container, so the distances will not change.</p>
<p>Edit: One more thing. When the problem says "the volume", they're referring to the volume of the gas, not necessarily the container. Since intermolecular forces would change the volume, the answer has to be E.</p>
<p>^ k sorry, I asked for help and I guess I shouldn't look a gift horse in the eye, but, that just made no sense.</p>
<p>Whether its ideal or not it takes up the entire container. Sencond, the volume of the gas is filling the volume of the container from the beginning, so that's not an issue. Third, if I were to assume that it isn't a real gas I'd be assuming that it were ideal. Thus look over your grammar.</p>
<p>Finally, I think that if the question specificaly brings intermolecular forces into one of the 3 items that it is supposed to be a real gas.</p>
<p>haha i took ap chem in tenth grade, and yes it is d just think about it. If the temperature cools, that means that the particles will be less active and will slow down, thus decreasing the space betweent them and decreasing the pressure against the container. Cheers</p>
<p>E) How will slower molecules make them closer together. If they are moving at 1000mph then its basically impossible to know where they are, so we just assume that they are random. If they are random always, one of the assertions of an ideal gas, then their average distances under constant volume will not change. The molecules do not take up the entire space, they occupy a small fraction of the space but their intermolecular forces causes them to stay apart from eachother, which makes them occupy a large space. I would put the answer as E, which should be the right one because you are not suppose to know about the "very technical stuff" that I dont know about. Its a high school question, not a college one. The molecular mass of the gas remains constant.</p>
<p>is this one of the harder chem questions because i am taking chem right now and i never considered taking the SAT or anything but if this is considered a "hard to medium hard question" theni will take it cause this question was easy</p>
<p>It is never possible to classify questions as easy, medium or hard that suits everyone. Even if you think this question is easy, so what? This is only one question. If you have never reviewed 1 or 2 SAT2 chem tests, you would not be able to tell how the test is. Similarily, scoring 800 in the first two practices does not guarantee 750+ on the real test. Seriously, think.</p>
<p>I am offended by your response, i go to a small (20 kids in my grade) public school and i take chemistry with a group of kids besides me and 5 others who plan to go into the army or work force. I plan to go to a four year, and the 4 others are planning on community college. I do not have a good education and was merely expressing my surprise that i might know any awnser on a higher leval chemistry test. obviously i will not know how the test is unless i practice and review, but i was asking in general about the question because at my first glance, it was not hard.</p>