The past several posts have been about gas laws. The Combined Gas Law does just what it says, the 3 gas laws combine as follows:
P V / T = P V / T
Again, temperature must be in Kelvins. This ensures that negative values and zero are not in the denominator of the fraction.
What is nice is that all 3 gas laws are neatly in this relationship -- all you have to do is eliminate (cancel) the constant variable. It's now worth it for a student to memorize because this relationship contains a lot of information.
As I taught my students, I would cover the T's to get PV = PV, cover the P's to get V / T = V / T , and cover the V's to get P / T = P / T. Very useful!
A very typical mathematical problem is to convert the volume of a gas sample with values of pressure and temperature to a volume at standard conditions of 1 atmosphere and 273 Kelvin (0 degrees Celsius).
You can algebraically rearrange the variables and then plug in the values for a solution; however, it is six variables and can get a little confusing. Plugging all variables with units and then solving algebraically is a very reasonsable method.
Here is a worksheet with solutions:
http://misterguch.brinkster.net/WKS001_007_146637.pdf
This video contains a discussion of molar volume of a gas, but then several demonstrations. It is longer (15 minutes), so you might want to skip ahead at times. I recommend wearing eye safety goggles while working with any of these demonstrations. I tend to err on the side of caution!
P V / T = P V / T
Again, temperature must be in Kelvins. This ensures that negative values and zero are not in the denominator of the fraction.
What is nice is that all 3 gas laws are neatly in this relationship -- all you have to do is eliminate (cancel) the constant variable. It's now worth it for a student to memorize because this relationship contains a lot of information.
As I taught my students, I would cover the T's to get PV = PV, cover the P's to get V / T = V / T , and cover the V's to get P / T = P / T. Very useful!
A very typical mathematical problem is to convert the volume of a gas sample with values of pressure and temperature to a volume at standard conditions of 1 atmosphere and 273 Kelvin (0 degrees Celsius).
You can algebraically rearrange the variables and then plug in the values for a solution; however, it is six variables and can get a little confusing. Plugging all variables with units and then solving algebraically is a very reasonsable method.
Here is a worksheet with solutions:
http://misterguch.brinkster.net/WKS001_007_146637.pdf
This video contains a discussion of molar volume of a gas, but then several demonstrations. It is longer (15 minutes), so you might want to skip ahead at times. I recommend wearing eye safety goggles while working with any of these demonstrations. I tend to err on the side of caution!
Check out my lab book "Chemistry on a Budget" at:
http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget
It contains a lab that collects a gas without a chemical reaction!
Each lab is presented with two possible report formats -- both with the same procedure -- one with 10 questions to be answered as a conclusion, the other with a full laboratory report required. This was to give the teacher the option of what type of report is desired!
*I'd love to hear from you about your experiences, your questions or if you have ideas for other topics for this blog.
Have a good week!
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