# Distance between molecules

#### songoku

1. The problem statement, all variables and given/known data

given that in a system, there are 5 % oxygen and 8 % nitrogen. it's also given the molecular mass of the two gasses. find the distance between molecules

2. Relevant equations

3. The attempt at a solution

i don't know what the percentage is for. is it the percentage of mass, volume, or mole?

i even don't see the connection between the data given and the question asked T_T

#### LowlyPion

Homework Helper
Maybe you should figure out how many molecules there are in a volume?

For any particular volume, of a given (molar) mass and %'s of objects (molecules in this case) with particular mass then how close together are they on average to fit in the volume?

#### songoku

how can we identify that the percentage given is molecules?

i suppose that the distance between the molecules is the distance between oxygen molecules and nitrogen molecules? or can it be the distance between oxygen molecules itself?

i guess maybe to get the answer is from volume. using V = 4/3 phi r^3, we find radius of oxygen and nitrogen molecules. then to find the distance, just simply add those radius

but i can't find the volume. From your idea, i should find the number of molecules and i even can't get there...

if the given data is percentage of molecules, i think we need to know how many molecules there are in the given system, but there is no such information on the question..

thx

#### LowlyPion

Homework Helper
Perhaps if you post the entire statement of the problem with the specifics?

#### songoku

i don't know the entire statement of the questions because i got it from friend and she also doesn't remember but all the specifics have been stated.

the information given are the percentage and the molar mass

#### LowlyPion

Homework Helper
i don't know the entire statement of the questions because i got it from friend and she also doesn't remember but all the specifics have been stated.

the information given are the percentage and the molar mass
OK then where is the other 87%?

What is the other 87%

What is the volume?

How many moles? Or failing that how many moles per liter?

Without the complete question - and I continue to think there is more than what you are getting second hand - I see little direction toward a solution.

#### songoku

hm... maybe the question isn't complete

so i conclude that based on the previous data, we can't solve the problem.

but is my idea right?

thx

#### LowlyPion

Homework Helper
hm... maybe the question isn't complete

so i conclude that based on the previous data, we can't solve the problem.

but is my idea right?

thx
Not exactly.

I think you want to look at it from the point of view of the number of objects in the overall volume. These are apparently gas molecules flying about and colliding. I think the radii of the molecules will turn out to be a lot smaller than the average distances. Hence the average distance will be more likely determined by the average volume of an object ... i.e volume / # items.

#### songoku

if the question turned out like this :

given that in a system there are 80 % of oxygen and 20 % of nitrogen. assume that the system in STP condition.

can we find the distance between molecules or we should know the volume of the system ?

so the distance between molecules = volume / number of molecules ?
but the unit will be m^3

will it be different if we take the shape of the volume to be cube and if we take sphere ?

Last edited:

#### LowlyPion

Homework Helper
will it be different if we take the shape of the volume to be cube and if we take sphere ?
Since you are not dealing with beach balls packed in a crate, I'd say so long as atomic volumes are << than the average m3 domains then I think a cubic box will more accurately determine their range. Since they are averagely placed in the boxes, then I'd describe their distances as merely (on average) the length of a side of a cube they are in.

#### songoku

ok, thx a lot lowlypion ^^

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