Ideal gas Question

Discussion in 'DAT Discussions' started by osimsDDS, Jun 3, 2008.

1. osimsDDS 5+ Year Member

Joined:
Jun 8, 2007
Messages:
925
2
Status:
Pre-Dental
Which of the following is true of an ideal gas?
a)the volume is independent of the pressure of the gas,
b)the pressure is inversely proportional to the number of moles of gas
c)the volume is directly proportional to the pressure of the gas
d)the volume is inversely proportional to the pressure of the gas
e)the pressure is independent of the number of moles of gas

Which one is it?

2. userah 7+ Year Member

Joined:
Aug 9, 2007
Messages:
555
0
Status:
Dental Student
D since it's for ideal gases no? PV = nRT?

Joined:
Jan 24, 2008
Messages:
168
0
Status:
Pre-Dental
C?

4. OP

osimsDDS 5+ Year Member

Joined:
Jun 8, 2007
Messages:
925
2
Status:
Pre-Dental
haha yea i dunno i was torn between those 2 choices, either c or d...

Isnt PV=k, if P increases then V must decrease so is that inversely proportional or directly proportional???

5. Glycogen 2+ Year Member

Joined:
Jan 24, 2008
Messages:
168
0
Status:
Pre-Dental
I think it will inversely proportional with Tem.I'm not sure,I would choose C.

6. OP

osimsDDS 5+ Year Member

Joined:
Jun 8, 2007
Messages:
925
2
Status:
Pre-Dental
found the answer on Wiki of course, best website on earth...

Boyle's law is one of the gas laws and basis of derivation for the ideal gas law, which describes the relationship between the product pressure and volume within a closed system as constant when temperature and moles remain at a fixed measure; both entities remain inversely proportional.

so: PV=k, inversely proportional
v/t=k, directly proportional (and also all others, the only one thats inversely is PV=k)

7. doc3232 7+ Year Member

Joined:
Feb 15, 2008
Messages:
3,809
9
Status:
Dental Student
False, this is the best site on earth...

8. OP

Joined:
Jun 8, 2007
Messages:
925
2
Status:
Pre-Dental
9. joonkimdds Senior Member 7+ Year Member

Joined:
Jun 30, 2005
Messages:
2,780
2
Status:
Pre-Dental

Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
#9
Last edited: Jun 4, 2008
10. Sea of ASH 2+ Year Member

Joined:
Sep 15, 2007
Messages:
254
1
a) V=nRT/P FALSE it is dependent
b) P=nRT/V FALSE they are directly proportional
c) V=nRT/P FALSE they are inversely proportional
d) V=nRT/P TRUE volume and pressure are directly proportional
e) P=nRT/V FALSE it is dependent

also if you notice the answer choices, once it says that P and V are independent, then inversely proportional, and then directly..... i HAS to be one of these right? process of elimination....

11. smile101 2+ Year Member

Joined:
Dec 4, 2007
Messages:
401
0
Status:
Pre-Dental
This is a very basic simple question and I don't understand why its taking so much discussion. D is def the correct answer. On the ADA guidelines, it says to know Boyle's and Charles law....so know them!!!

12. joonkimdds Senior Member 7+ Year Member

Joined:
Jun 30, 2005
Messages:
2,780
2
Status:
Pre-Dental
Volume is inversely proportional to pressure,
volume is directly proportional to the number of moles of gas,
so why is the pressure proportional to the number of moles of gas?
I don't know where i am getting confused.

Stop hovering to collapse... Click to collapse... Hover to expand... Click to expand...
13. ucla2134 7+ Year Member

Joined:
Nov 19, 2006
Messages:
785
1
Status:
Pre-Dental

The pressure and volume is proportional to the number of gases and why the hell the pressure is inversely proportional to the volume? It is happen when you keep other variables constant in the Ideal gas law:
For example, the Avogado law n/V=constant happen when the Pressure and Temperature is keeping constant. Same thing is if you keep Volume and Temperature constant, then you get pressure proportional to the number of moles.

14. creative8401 Im Anush Hayastan 2+ Year Member

Joined:
Jan 22, 2008
Messages:
202
2
Status:
Pre-Dental
Hi everybody. Hope everyones doing well. Let's take a look at this question. Many of the students have responded correctly, but I'd like to add a bit explanation to their correct answer for those confused.

A) The volume is independent of the pressure of the gas
PV = nRT; and the volume cannot be independent of the pressure. It would be best to think of real life examples, as it will make it easier to understand the question. If you have ever tried to fill a balloon, one knows that the pressure and volume are related to one another. One time I tried to fill those air beds by mouth, and since the volume of the bed is big, a lot of gas molecules have to be blown into it to increase the pressure; thus they are related to each other (not to mention I was about to faint afterwards).

B) The pressure is inversely proportional to the number of moles of gas
Inversely...wow. This would mean that if you put more air molecules into a tire, the tire would go flat. Makes no sense. They are directly related, if you put more moles (hence more molecules) of a given gas, the pressure would increase. This is why we have tired, and balloons.

C) The volume is directly proportional to the pressure of the gas
Boyles Law: They are indirectly related. The formula is P1V1 = P2V2, and P1V1 = Constant; Therefore, in order to obtain the same constant each time, when one increases the other factor would have to decrease. Real life analogy: You increase the volume of the thoracic cavity, the pressure drops and air rushes into your lungs.

D) The volume is inversely proportional to the pressure of the gas

E) The pressure is independent of the number of moles of gas
This is a funny one. For those of you who have had a balloon blow up in your face, you very well know that the more you fill it, the larger the pressure, until the elastic walls give way.

My suggestion would be to think of these types of questions in a more realistic fashion. Once you can do this, then the concepts are easy to understand, and the formulas...well, they are just ways to complicate simple concepts.

15. Dencology 2+ Year Member

Joined:
Mar 7, 2008
Messages:
396
0
Status:
Pre-Dental
Hey creative.
Good job man. i was gone post something like this. lately, a lot of people don't know what they are posting and they post incorrect answers. please know your fact cold before you post something. Volume and Pressure is inversely related to each other. if you have a a cylinder and you decrease its volume, now there is less room for the molecules to move around and they are exerting more pressure to the walls and to each other. therefore, as you decrease volume you increase pressure. it is very simple.

16. Sea of ASH 2+ Year Member

Joined:
Sep 15, 2007
Messages:
254
1
this is exactly PV=nRT

17. pasionatdentist 2+ Year Member

Joined:
Dec 30, 2007
Messages:
97
0
Status:
Pre-Dental
D>>>>> pressure is inversely proportional to volume.... just learned it in kaplan class

18. userah 7+ Year Member

Joined:
Aug 9, 2007
Messages:
555
0
Status:
Dental Student
just look at the formula guys. you can figure out every rule based on the formula for ideal gases.

If P increases, the only way to keep everything else constant is to decrease V. Thus they are inversely related. And for temperature. Since they're on opposite sides, increase in P means increase in T as well so they are directly proportional. Same goes for volume and temperature; directly proportional.

We’ve been on the Internet for over 20 years doing just one thing: providing career information for free or at cost. We do this because we believe that the health education process is too expensive and too competitive.

We believe that all students deserve the same access to high quality information. We believe that providing high quality career advice and information ensures that everyone, regardless of income or privilege, has a chance to achieve their dream of being a doctor.