What Is the Diffusion Coefficient of Odour Molecules?

AI Thread Summary
The discussion revolves around calculating the diffusion coefficient of odor molecules based on a scenario in a chemistry lab. The student initially calculates the time taken for the odor to travel 3 meters and then 2 additional meters, ultimately arriving at a diffusion coefficient of 0.02136. However, this value conflicts with the textbook answer of 0.044, prompting a request for clarification on the calculations. Participants point out confusion in the student's approach, particularly regarding the equations used and the interpretation of distance ratios. The conversation emphasizes the importance of correctly applying the diffusion equation and understanding the relationship between distance and time in diffusion processes.
HelpaSista
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Homework Statement



A student working 3.0 m away from you in the chemistry lab creates a bad odour. The odour takes a while to get to you (assume that air currents are negligible). You then move 2.0 m further away, but the odour catches up with you in another 60 seconds. What is the diffusion coefficient of the molecules you smell?

hint: the root mean square distancee and the time must be measured from the source of the diffusing molecule.


Homework Equations



t= R^2 / 6D


The Attempt at a Solution



I first tried to find time from 0-3m by using the ratio between the two distances

2^2 / 6*s X 6T/^3 = 1 (1 since D is the same)

I found that t = 135s

I then added 135 to 60 seconds and used that as my total time and 5 as my total R and solved for D

D = R^2 / 6*T

= 25 / 6*195

=0.02136


However, my textbook says the answer is 0.044 and I don't see what I am doing wrong. :(

Any help will be much appreciated, thank you!
 
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HelpaSista said:

Homework Statement



A student working 3.0 m away from you in the chemistry lab creates a bad odour. The odour takes a while to get to you (assume that air currents are negligible). You then move 2.0 m further away, but the odour catches up with you in another 60 seconds. What is the diffusion coefficient of the molecules you smell?

hint: the root mean square distancee and the time must be measured from the source of the diffusing molecule.


Homework Equations



t= R^2 / 6D


The Attempt at a Solution



I first tried to find time from 0-3m by using the ratio between the two distances

2^2 / 6*s X 6T/^3 = 1 (1 since D is the same)
It is not at all clear how you got this equation. What does it have to do with the ratio of the two distances? What is the "T/^3" supposed to mean, that combination of symbols makes no sense?

I found that t = 135s

I then added 135 to 60 seconds and used that as my total time and 5 as my total R and solved for D

D = R^2 / 6*T

= 25 / 6*195

=0.02136


However, my textbook says the answer is 0.044 and I don't see what I am doing wrong. :(

Any help will be much appreciated, thank you!
 

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