Kinetic Theory of Gases - A-level Physics 

What 28 dislikes, i see no dislikes. Isnt the world such a nice place without dislikes, everyone likes everything now. Fabulous

nah its bad this way cause imagine if we clicked on a trash vid but we had to wait a solid 5 mins to realise it rather than have the like dislike ratio tell us beforehand@@namename3130

How did it go?

Callum Grimes guilty 😂

Same here. I have a strong feeling Gases will come up tomorrow

Absolutely shitting myself Grimes XD! good luck ladies and gents!!

me im super anxious

Hope this comes up the only thing I know😭😭😭😭

Other types of gasses store energy in molecular rotation and vibration, which is why molar heat capacity isn't identical for all types of gas. Otherwise it would be.

Yes. But by using the time between collisions, we are calculating the average force a particle exerts as it goes from one end of the box to the other.

​@@ScienceShortssir , the time between collisions should be l/u ? Why is it taken as 2l/u , please tell sir.

@@abbasmehdi2923 this might be late lol but its because we consider the particle going TO AND FROM the cube so it travels the twice the length

Ikr

That's literally what I was about to comment... Makes no sense to me :(

wtf this is so true

The cube is only to derive the formula. This can then be applied to any container.

It gives the average force exerted by a particle.

Its not quite asked or useful the only questions asked are about what the symbol c means

When the gas is in equilibrium , molecules moves entirely random. So all the direction of motions are equally probable. so , u(mean square)=v(ms)=w(ms)=( u^2+v^2+w^2)(mean)/3=c(ms)/3

It's because change in momentum is calculated by momentum *after* - momentum *before* . So if a particle is initially travelling at v and ends up travelling at -v, then the change in momentum is (m)(-v) - (m)(v) = -mv - mv = -2mv. Hope that helps?

Change of any physical property is (after)-(before), so it is negative

I had the same question, thanks people in the replies :)

​@@DelboiixHello , shouldn't time be l/u instead of 2l/u for one collision. Why 2 is there ? Also , if particle hits one wall , why are we taking whole area of six faces

To get the total mass of all the molecules we do this.

Time of their actual collisions. While they are together colliding. Compared to time they are apart and not in a collision

Yes, you've got it 😊

@@ScienceShorts cool thanks! 😊

c (rms) is an average speed that takes into account of all 3 different directions🙃

Kaishary Islam this for aqa

Please if u alr done ur alevels and get this please pelase explain it to me, I keep rewatching it and I don’t get it

@@user-ej6we6ei7q momentum is a vector quantity change in momentum would be final momentum - initial momentum consider momentum to the right as positive, then final momentum = -mu1, initial momentum is mu1 hence change in momentum = -mu1-mu1 = -2mu1 then rate of change of momentum = -2mu1/t

If u look at 5:10 dimension lx is already included in the equation for force. Given that pressure=F/A, A=lylz and this combines with lx which is already in the force equation to give lxlylz which is the volume.

same

aavash devkota (I) : pV = nRT 4 x 10^5 x 0.7 = n R x 288 n = (4x10^5 x 0.7)/(R x 288) and just type that into your calculator

1 year late.. lol but for the second part you can use equation pV=1/3Nm(crms)^2 Use the value of moles you got in part 1 nR=Nk Rearrange nR/K =N Then find mass of oxygen: Relative molecular mass x moles= mass Insert values into equation : (pV/(3)Nm) =(crms)^2 Square root answer And then you have (crms)

The cube is only a model we use to derive the equation. It still holds true for any container, as there will always be as many particles going up, down, left, right etc.

@@ScienceShorts Omg, thank you so much 😭 I was being stupid, I was looking at the equation for average Force overtime and wonder why on earth could F be equal in each x,y,z case if the length of each side is not equal. Turns out you were talking about Pressure and only after dividing the equation by Area did we generalize the velocity square average!! Thank you so much for the video and for your reply !!

@@ScienceShorts I usually see this derived using calculus conventions, using dx, dy, dz differential elements instead. Your method is mathematically equivalent, without confusing students who may not be familiar with deriving things using calculus.

i had the exact same question

well before anything i think he meant to represent the gas as a whole by just that one partical...but again he also mentioned that there are many other individual particals and he was clearly referring that while deriving the equation so i am as confused as you

Sir yes sir.

ARE YOU FROM KINGSMAN

Imma just remember the cube ngl

lmfao pls?

?

No, it means the force exerted by one molecule on a face lylz.

@@ScienceShorts So if I punched a gigantic wall that gigantic area, does that mean the pressure I exerted is P=F/Area of the entire wall ? Contradictory to what we've learnt about pressure isn't it?

@@ferdousreza6907 There's billions of gas molecules. This is simply the force on one face of the container, due to the "average" gas molecule. I.e. the gas molecule moving at the RMS speed specifically.

This is so we get the maximum time within which the collision happens. To get the average force, we need to take the change in momentum and divide by the total time this happens over, seeing as the impact time itself would be infinitesimal.

​@@ScienceShorts I think he still deserves a clear answer to his question, especially given the emphasis placed on the fact that collision duration

m is the mass of the single molecule. so Nm is the total mass of the substance divided by V gives the density

yea i just realised doing Np (p=density) gives the same as Nm/v

M/V here M is mass of gas which is equal to n×m(n=no of molecules,m= mass of each molecule) so nm/V= M/V

Woah! Why didn't I think of that?! 😄

yeee

RT-Viz the kinetic theory model?

ManasChaubey for aqa yes

no u dont, its given in the data sheet

We're only concerned with the magnitude.

idiot

Can someone answer this please

@@Holly-ew7ps cos change in p = final p - inital p. Initial p = mu, Final p = m(-u) = -mu (because the final velocity is in the opposite direction of 'u', thereby '-u') So change in p = -mu - mu = -2mu 🙃

😇🤪🤭

@@mrk2938 LOOL

If you multiplied the 1/3crms^2 = kT by 3, you get crms^2 = 3kT. so then you put crms^2 into the second equation, which is 1/2crms^2, meaning you halve the 3kt, making it 3/2kT. I'm not sure if I explained it well.

Because we just care about the size of the force, not the direction.

@@ScienceShorts and why is that so pleasee??

@@krishnabhambhani5270 We can account for dropping the negative sign using Newton's third law. -2mv/t is the force needed to change the momentum of the molecule and so is provided by the wall and acts on the molecule. The force on the wall, using Newton's third law. is equal in size and opposite in direction. This means that the force we want is positive.

@@peterwilde4022 so that means -ve force (due to direction) = +ve force? If relating to Newtons 3rd law??

And if yes how does it apply to the single moving particle's momentum because if the particle goes in a direction w momentum mv and comes back with the same momentum but with -ve momentum (-mv) wouldn't it be mv + (-mv) which is 0

It's physics not maths

Boo. Nerd. Go back to blackpenredpen.

How did it go

@@sosman747 decent , thx for asking

@@tbobxtbob bruh. Thanks for answering. Most just leave such comments and then don't respond