# Calculation of average molecular speed

• Chemistry
In summary, the conversation discusses calculating average speed using a formula and the importance of using consistent SI units. The formula provided is based on the ideal gas law and takes into account the mass of the molecules or atoms. It is important to convert all values to SI units in order to get an accurate answer.

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?

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.

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