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# Kinetic Energy of Molecule

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1. Question

I thought KE = 3RT/2Na, so why aren't they dividing by Avagadro before finding the root?
2. OK - I am going to claim the mark scheme is wrong on this one - it's a practice paper, but I'd really like if someone could either agree or disagree with me on this one.

My logis is this - 1 bar of pressure (e.g. water in a central heating system) is about 100kPa - the question talks about a gas at 120kPa., so we are talking about similar pressure. They give an answer of 1,340 m/s, which means that any molecule would be travelling at almost 1 mile per second - just in my head that seems way too fast. This means in a pipe of diameter of 10cm, a molecule could go back and forth across that pipe 13,400 times in 1 second based upon the mark scheme answer.
3. MASS= n x MOLAR MASS
n=N/NA
so that means that Mass=N/NA x Molar mass
Using 0.5 M Crms^2=3/2 R/NA T.
You will have to rearrange the equation to get NA x Mass. So the NA will cancel out. N=1 so you just have to divide by Molar mass. I think
4. Kelly's working is correct. Don't be put off by the speed of the molecules
5. That's great - got it now, and understand - cheers.
6. Posted as separate question

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