# Thermal physics help again

https://i.gyazo.com/16dd3e33a892b7b1f1f9b7ac79744875.png
Um for the last question, is there a more efficient way of doing it. Would appreciate help for this question..

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More efficient compared with what?
Original post by Sinnoh
More efficient compared with what?

Like I got the answer right but I done a long winded method for only a 2 marker ... just want to know how they got this in the mark scheme
not sure how they got this but I'm guessing it is something to do with pv=1/3Nmcrms^2?
N=Number of molecules
I just used V as constant for both helium and nitrogent, Number of molecules N as equal to 2N,R=R,T=T
For nitrogen I done:
V=V, N=N, R=R,T=T,
I made equations p1 and p2 for both helium and nitrogen and added them together which should equal to 120kPa and then solved for V which I can then use in the helium section for p which I got as 80kPa.
(edited 1 year ago)
Original post by Sinnoh
More efficient compared with what?

Haha, I get it now it's just a ratio of 2:1:3 to helium and nitrogen and since the total pressure is 120kPa, all I have to do is just multiply 2/3 to 120kPa which should give me 80kPa. I figured it out yay.
(edited 1 year ago)
Original post by Behemouth
Like I got the answer right but I done a long winded method for only a 2 marker ... just want to know how they got this in the mark scheme
not sure how they got this but I'm guessing it is something to do with pv=1/3Nmcrms^2?
N=Number of molecules
I just used V as constant for both helium and nitrogent, Number of molecules N as equal to 2N,R=R,T=T
For nitrogen I done:
V=V, N=N, R=R,T=T,
I made equations p1 and p2 for both helium and nitrogen and added them together which should equal to 120kPa and then solved for V which I can then use in the helium section for p which I got as 80kPa.

Each 'species' of particle has the same temperature, same physical constants, the only difference is the number of them. So each species in the gas contributes its own pressure. If two thirds of the particles are nitrogen, nitrogen contributes two thirds of the pressure.
Original post by Sinnoh
Each 'species' of particle has the same temperature, same physical constants, the only difference is the number of them. So each species in the gas contributes its own pressure. If two thirds of the particles are nitrogen, nitrogen contributes two thirds of the pressure.

yeah I just figured that out, I just made a ratio of 2:1 and figured it out. Thanks for your help. I know it's meant to be obvious that volume is constant but I'm not sure why volume in this case is a constant?
Original post by Sinnoh
Each 'species' of particle has the same temperature, same physical constants, the only difference is the number of them. So each species in the gas contributes its own pressure. If two thirds of the particles are nitrogen, nitrogen contributes two thirds of the pressure.

you mean helium
Original post by Sinnoh
Each 'species' of particle has the same temperature, same physical constants, the only difference is the number of them. So each species in the gas contributes its own pressure. If two thirds of the particles are nitrogen, nitrogen contributes two thirds of the pressure.

not sure why volume is constant, it's quite hard to think about
Original post by Behemouth
not sure why volume is constant, it's quite hard to think about

Because gases fill the volume of the container they're in
Original post by Sinnoh
Because gases fill the volume of the container they're in

Ah, I confused myself I thought you just had to take into account of the volumes that nitrogen and helium each occupies..
Original post by Sinnoh
Because gases fill the volume of the container they're in

Wait so are you saying that both the helium and nitrogen are both occupying the total volume V? Are you just assuming that the helium occupies volume V and nitrogen occupies volume V as well???
Original post by Behemouth
Wait so are you saying that both the helium and nitrogen are both occupying the total volume V? Are you just assuming that the helium occupies volume V and nitrogen occupies volume V as well???

Yes, because that's what gases do - whatever container they're in, that's their volume.
Original post by Sinnoh
Yes, because that's what gases do - whatever container they're in, that's their volume.

Right, I just overcomplicated it haha. Thank you for helping me. Got tips on how to ace physics paper 2? I'm just trying to do practice questions on concepts I overcomplicate
(edited 1 year ago)
Original post by Behemouth
Right, I just overcomplicated it haha. Thank you for helping me. Got tips on how to ace physics paper 2? I'm just trying to do practice questions on concepts I overcomplicate

Np. Put it this way: in the earth's atmosphere there's an equal volume of nitrogen, oxygen, argon etc.
Original post by Sinnoh
Np. Put it this way: in the earth's atmosphere there's an equal volume of nitrogen, oxygen, argon etc.

sorry to annoy you but I understood what you explained to me but that doesn't make sense the analogy you gave since nitrogen takes up 78 percent of the air.. and there's different percentages so wouldn't that cause them to take up a different amount of volume?... I know what am saying doesnt make sense
Original post by Behemouth
sorry to annoy you but I understood what you explained to me but that doesn't make sense the analogy you gave since nitrogen takes up 78 percent of the air.. and there's different percentages so wouldn't that cause them to take up a different amount of volume?... I know what am saying doesnt make sense

They each take up w different percentage of course, but the total volume is constant. When you make equations equal, its because we assume no volume of gas leaves the system.
Original post by itslitbro
They each take up w different percentage of course, but the total volume is constant. When you make equations equal, its because we assume no volume of gas leaves the system.

Oh hello it's you again. Okay, that makes sense. thank you. sorry for being annoying you guys
(edited 1 year ago)
Original post by itslitbro
They each take up w different percentage of course, but the total volume is constant. When you make equations equal, its because we assume no volume of gas leaves the system.

Original post by Sinnoh
Np. Put it this way: in the earth's atmosphere there's an equal volume of nitrogen, oxygen, argon etc.

Thanks for the help guys
Original post by itslitbro
They each take up w different percentage of course, but the total volume is constant. When you make equations equal, its because we assume no volume of gas leaves the system.

how does potential energy relate to intermolecular forces for an ideal gas?
Original post by Behemouth
how does potential energy relate to intermolecular forces for an ideal gas?

It doesn't