Chemistry Calculation of average molecular speed

AI Thread Summary
The average molecular speed can be calculated using the formula uavg=sqrt(8PV/πnM), but it is crucial to use consistent units. The user initially plugged in values with incorrect units, leading to an erroneous result. It is recommended to convert all values to SI units, specifically using pressure in Newton/m². The formula derives from the kinetic theory of gases and incorporates the ideal gas law, emphasizing the importance of proper unit conversion. Ensuring unit consistency is essential for accurate calculations in molecular speed.
subhradeep mahata
Messages
120
Reaction score
13
Homework Statement
Calculate the average speed of 2 mol oxygen molecules at pi*10bar pressure occupying 8 litres volume.
Relevant Equations
Given in the "Attempt at a Solution" section
We can calculate the average speed using this formula: uavg=root(8PV/ΠnM)
I plugged in the following values:
P= pi*10 atm (bar is approximately equal to atm)
V=8lts
n=2mol
M=32*10^-3kg/mol
But it is giving wrong answer. Can you tell me what went wrong?
 
Physics news on Phys.org
Is this a joke or do you just want someone to do your homework for you? You ask "what went wrong" but don't show what you did nor what answer you got!
 
Units?
 
@HallsofIvy Actually I am pretty sure that I plugged in values having wrong units, that's why I just showed the values and what formula I am using. I just wanted to know what units are to be used in the formula.
 
@mjc123 Yeah probably. Can you tell me what units should I use?
 
Consistent ones. I would convert everything to SI units.

The one thing you must never do is blindly plug numbers into a formula without consideration of units, e.g. mixing atm, L, kg etc. (some SI and some not).
 
Suggest you use SI units. The pressure ## P ## needs to be in ## Newton/m^2 ##. ## \\ ## The formula you have comes from ## \bar{v}=\sqrt{\frac{8 k_bT}{\pi m}} ##, where ## m ## is the mass of the molecule or atom. ##\\ ## Meanwhile, with the ideal gas law ## PV=n R T=N k_b T ##, where ## N=## number of molecules, so that ## N=n N_A ## where ## n =## number of moles, and ## N_A=## Avagadro's number, we can write ## \bar{v}=\sqrt{\frac{8 PV}{\pi n M}} ##, where ## M=m N_A ##, is the mass of a mole of atoms or molecules.
 
Last edited:
Back
Top