[nikita]

I'm sorry if Ive titled this wrong, but I am in the chapter with gases and kinetic molecular theory.  I am doing this endless amount of Mastering Chemistry questions and sometimes they are a little more advanced or do not even show up in my text.  It is also quite possible that I do not understand the question.     I cannot find an example or a problem in the book that is remotely like this question, so I cannot post how I have tried to solve it, because I havent.  I am definitely looking for a point in the right direction so I can learn how to solve this problem.  I do not understand what is meant by "air that would be displaced."  what air?  the air in the closet?  i cant even begin to ask questions on this because I do not understand the question. 


A 1.3 L container of liquid nitrogen is kept in a closet measuring 1.2m by 1.2m by 2.0m. Assuming that the container is completely full, that the temperature is 28.1 C, and that the atmospheric pressure is 1.1 atm, calculate the percent (by volume) of air that would be displaced if all of the liquid nitrogen evaporated. (Liquid nitrogen has a density of 0.807g/mL .)

Any hints at all will be appreciated and worked on.

[Borek]

Either it is a trick question, or I don't understand it. What happens when the liquid nitrogen evaporates?

[nikita]

well, i m clueless as well, but if you are, then im pretty screwed.    It could very well be a trick question, but I think the questions in mastering chemistry have to be answerable.  My problem is Im not even sure what the question is.  Its not due until tuesday at midnight, i think, but I really just wanted to learn how to do it.  I could ask my recitation prof, but she is usually hard to comprehend.

ok, i just realised its due at 3 am on tuesday, so i will not have recitation before then.  i will have lecture, but i hate talking to my prof about things i dont understand, because i dont want him to think im dumb.  i have an A in gen chem right now and I dont want to sway his view of me.  I can, however, ask for hints on the questions, but I will lost points.  I guess thats better than not answering it at all.

[Borek]

What are your thoughts as of now?

[nikita]

my thoughts are i dont know what air they are talking about.  i dont know anything about displacement and i have never learned about if before.  i have googled gas laws and displacement and i have come up with nothing.  i see that the volume of the closet has something to do with it as well as the density of liquid nitrogen.   i dont know what i am comparing to what.  the liquid nitrogen evaporates into N₂ gas?  i dont know what the closet volume has to do with the problem.  am i to liken it to the container?  like 1.2 L of liquid nitrogen is in a 2.88m³ container?  am i to find out the volume of N₂ gas in a 2.88m³ container? 

or could this be some kind of effusion problem?  no.  i frankly have no clue.  I looked in the index of my test for displacement and it doesnt appear in the book.  maybe displacement has nothing to do with the problem.  sorry about this stream of consciousness, i thought maybe something would jump out at me, but alas nothing.

[Borek]

Displacement means that part of the volume originally occupied by one thing becomes occupied by the other. Trick is, by definition each gas occupies whole volume, no matter what other gases are present in the container. Not only it occupies whole volume, but it also has a constant partial pressure. When you add other gas it will have its own partial pressure, it will occupy whole volume as well, and the total pressure will be sum of partial pressures.

So for me gas is not displaced. You may calculate displacement assuming that the closet is divided by the movable piston that separates gases; but that's not part of the question.

[nj_bartel]

I agree Borek - trick question.

[nikita]

so, i guess my question is, is the liquid nitrogen evaporating into nitrogen gas, and i am just trying to find out the volume of gas occupied by the nitrogen gas?  is the whole volume of the box just extra info?

[nikita]

or do i find the mols in the container of liquid nitrogen and then apply that to evaporating into a gas in the closet, if that makes sense.  because if the liq nitrogen is evaporating, its evaporating into the closet, and thus the closet isnt 1.3L, it is however many mols of liq nitrogen that were in the 1.3 L container and are now in the closet  .

[nikita]

yeah that doesnt work, i get a huge number.

[nikita]

too much info sidetracking me in that prob.  29%, very easy.  thank you.