# Calculation of average molecular speed

• Chemistry
• subhradeep mahata
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.
subhradeep mahata
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.

Last edited:

## What is "average molecular speed"?

"Average molecular speed" refers to the average velocity of molecules within a substance. It is calculated by taking the sum of all molecular velocities and dividing it by the total number of molecules.

## How is average molecular speed calculated?

Average molecular speed can be calculated using the root mean square (RMS) velocity formula, which takes into account the individual velocities of each molecule and their corresponding masses. The formula is: √(3RT/M), where R is the gas constant, T is the temperature in Kelvin, and M is the molar mass of the gas.

## What factors affect the average molecular speed?

The average molecular speed is affected by temperature, pressure, and the molecular weight of the substance. As temperature increases, the average molecular speed also increases. Higher pressure can also increase the average molecular speed, while a heavier molecular weight will result in a lower average molecular speed.

## Why is the calculation of average molecular speed important?

The calculation of average molecular speed is important in understanding the behavior and characteristics of gases. It helps determine the rate of diffusion and effusion, as well as the kinetic energy of molecules. This information is crucial in various scientific fields such as chemistry, physics, and atmospheric science.

## Can the average molecular speed of a substance change?

Yes, the average molecular speed of a substance can change depending on the conditions it is subjected to. As mentioned before, temperature, pressure, and molecular weight can all affect the average molecular speed. Additionally, the presence of other substances or external forces can also alter the average molecular speed.

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