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# Physics gas equations hwk help Watch

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1. Hi,

I'm a bit stuck with a couple of questions because I'm getting a bit confused about which formulae to use.

1. Hydrogen molecule. Molar mass-0.002Kgmol-1. Temperature= 273k

Calculate mean kinetic energy.
Calculate root mean square speed.

2. Air consists of mostly nitrogen and oxygen in proportions 1:4 by mass. Demonstrate that the Crms^2 of a nitrogen molecule in air is 1.07 times that of oxygen in same sample.

Molar mass: Nitrogen: 0.028 Oxygen: 0.032

Thanks
2. Bump
3. (Original post by VioletPhillippo)
Hi,

I'm a bit stuck with a couple of questions because I'm getting a bit confused about which formulae to use.

1. Hydrogen molecule. Molar mass-0.002Kgmol-1. Temperature= 273k

Calculate mean kinetic energy.
Calculate root mean square speed.

2. Air consists of mostly nitrogen and oxygen in proportions 1:4 by mass. Demonstrate that the Crms^2 of a nitrogen molecule in air is 1.07 times that of oxygen in same sample.

Molar mass: Nitrogen: 0.028 Oxygen: 0.032

Thanks
1) Using the temperature determine the mean kinetic energy. (There's a simple equation for that in the textbook with a 3/2 in it)
Use the equation (mean kinetic energy)=0.5*mass*(root mean square speed)^2 to find the root mean square speed

2) Equate the kinetic energies of nitrogen and oxygen using the eon above, plug in the mass
4. (Original post by MathMoFarah)
1) Using the temperature determine the mean kinetic energy. (There's a simple equation for that in the textbook with a 3/2 in it)
Use the equation (mean kinetic energy)=0.5*mass*(root mean square speed)^2 to find the root mean square speed

2) Equate the kinetic energies of nitrogen and oxygen using the eon above, plug in the mass
Thanks, I've done no. 1 now but I think I'm still doing no. 2 wrong as I can't seem to get to 1.07.
5. (1/2)*0.028*v^2=1/2*0.032*c^2
8/7c^2=v^2
v=sqrt(8/7)c
=2sqrt(2/7)c= 1.069044...c
roughly 1.07c
therefore
v/c is roughly 1.07
6. (Original post by MathMoFarah)
(1/2)*0.028*v^2=1/2*0.032*c^2
8/7c^2=v^2
v=sqrt(8/7)c
=2sqrt(2/7)c= 1.069044...c
roughly 1.07c
therefore
v/c is roughly 1.07
Thanks, I was trying to do it without labelling one as v and one as c so I understand it much better now

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