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Ideal Gas Law

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world_peace0's picture
Joined: Jan 2008
Ideal Gas Law

Three gas laws that describe the behavior of gases as revealed by experimental observations are:

Boyle's Law: V1P1=V2P2 at constant T and n

Charles's Law: V1T2=V2T1 at constant P and n

Avogadro's Law: V1n2=V2n1 at constant T and P

These relationships, which show how volume of a gas depends on pressure, temperature, and number of mles of gas present, can be combined as followed: V= R(Tn/P) where R is the combined proportionality called the universal gas constant. When the pressure is expressed in atmospheres and the volume in liters, R has the value 0.08206 L*atm/K*mol. The preceding equation can be rearranged to the more familiar form of the ideal gas law: PV=nRT.

1. A gas has a pressure of 3.2 atm and occupies a volume of 45 L. What will the pressure be if the volume is compressed to 27L at constant temperature?

2. The volume of a gas (held at constant pressure) is to be used "as a thermometer." If the volume at 0.0 degrees C is 75.0 cm^3 what is the temperature when the measured volume is 56.7 cm^3?

3. If a 16.6 L sample of gas contains 9.2 moles of F2, how many moles of gas would there be in a 750 mL sample at the same temperature and pressure?

4. A 11.2 sample of gas id determined to contain 0.50 moles of N2. At the same temperature and pressure how many moles of gas would there be in a 20 L sample?

5. Consider a 3.57 L sample of an unknown gas at a pressure of 4.3 x 10^3 Pa. If the pressure is changed to 2.1 x 10^4 Pa at a constant temperature, what will the new volume of the gas be?

6. Calculate the volume occupied at 87.0 degrees C and 950 torr by a quantity of gas which occupied 20.0 L at 27.0 degrees C and 570 torr.

7. A quantity of gas at 27.0 degrees C is heated in a closed vessel until the pressure is doubled. To what temperature is the gas heated?

8. A sample of gas occupies 3.8 L at 15 degrees C and 1.00 atm. What does the temperature need to be for the gas to occupy 8.3 L at 1.00 atm?

9. Calculate the volume of 02 present in a sample containing 0.89 moles of 02 at a temperature of 40degrees C and a pressure of 1.00 atm.

10. A sample containing 0.35 mol argon gas at a temperature of 13 degrees C and a pressure of 568 torr is heated to 56 degrees C and a pressure of 897 torr. Calculate the change in volume that occurs.

(Basically, my situation is that I have never taken the prerequisites to be in Chemistry Ap, and also I came in late into the school year as well so I really dont have a clue of whats going on. So the teacher gave me this worksheet on the side, which is something the class has already discussed during the beginning of the school year. I need help since I do not know how to do this, and I dont really want you all to just give mem the answers, but help me understand how to do them. They're due tomorrow and I'm a little clueless, so if you can please help me I'd really appreciate it.)

starlit2006's picture
Joined: Mar 2007

basically the gas law problems are really just a plug-in-the variable problem. Just make sure that before plugging in the variable that the variables are in the right units first (that means that pressure must be in atm and volume in L---if it helps set up your equation with your labels so that you make sure your variables are the same and that labels cancel to get you the right equation)

For example: Problem number 1
constant Temperature is Boyles law so you would use the eq P1V1=P2V2

P1=3.2 atm

divide by 27L >>>>>>label L cancels
>>>>>>sig. figs (your answer should be rounded to the least accurate number of digits..in this case it is 2 sig figs)

final answer: P=5.3atm

So that is the most basic of the problems....
I've looked through some of your problems and while some have the basic setup as the one I did above, others are just a tad bit harder.
But again, it all involves plugging into the equation.

The combined gas law that you listed below can better be rewritten as PV=nRT to keep the eq looking simpler and less intimidating.
R is always the constant 0.08206 L*atm/K*mol
T is the temperature ---make sure this is in Kelvin and not Celsius (to convert from Celsius to Kelvin just add the Celsius degrees to 273.15)
P is pressure ----make sure this is in atm (torr is the same as atm, there is 760mmHg in 1 atm)
V is volume ---make sure this is in L
n is the mole number (I'm not sure if you know what a mole is, basically you are given a number of grams for a compound and you have to convert that to moles; for example if you have 9 grams of H20 and you need to convert that to moles, well what you do is you divide the number of grams by the molar mass of 1 mole, to figure out the molar mass of 1 mole is pretty easy, all you have to do is to add up the atomic weights of the compound (in this case this is H20---the atomic weight is the bottom number of the periodic table) so 9grams of H20/18.0152grams H20=about 1/2)

hope this is helpful, sorry if this is brief but I have a load of homework to work through

if you need more help just email me at [email protected]" class="bb-email">[email protected] or just comment back here

johnfernandis's picture
Joined: Jun 2011

The ideal gas law can be viewed as arising from the kinetic pressure of gas molecules colliding with the walls of a container in accordance with Newton's laws. But there is also a statistical element in the determination of the average kinetic energy of those molecules. The temperature is taken to be proportional to this average kinetic energy...

dannsalik's picture
Joined: Jun 2011

Hi, simply if we are talking about ideal gas laws so these are only three main laws
1: Boyl's Law
2: Charles Law
3: Avogadro Law

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