[RapterBoyDD]

I need help with this answer i know it's easy but not for me.

100 mL of a gas is heated from 22 c to 100 c . What is the new volume of the gas?
So this is what i did

 2
V  = (100mL) (273k)
        -----------------
            2.73 Volume

It's this right or wrong ?
If its wrong can you plz point out were i got it wrong

[Borek]

Hard to tell what you did.

What law describes how the volume of the ideal gas depends on the temperature? Can you write it?

[MN1988]

pressure is constant so use Charles' Law.

V1/T1 = V2/T2

temperature has to be in Kelvin

[AdiDex]

How did you put the values in the that relationship .?
Did you convert temperature in kelvin from Celsius..?

[MN1988]

all gas laws use Kelvin as temperature.
t1 = 273+22=295
t2 = 273+100=373

100/295=v2/373

sorry for late reply - i only check this every few days

[AdiDex]

Bro ,
You done it correctly..

[MN1988]

If that is answered I have another question. I found this:

In which gas sample do the molecules have the greatest average kinetic energy?
A. H2 at 100 K
B. CH4 at 273 K
C. H2O at 373 K
D. CH3OH at 353 K

I haven't a clue how I would even go about this. I know the average kinetic energy is proportional to absolute temperature by assumption 5 of kinetic theory, but I don't know how that affects different gases composition.

Any help would be appreciated.

[mjc123]

You've answered it - the average kinetic energy is proportional to the absolute temperature. The identity of the molecules is irrelevant.

[MN1988]

Ah a trick question - cheers for the reply.
But I'm afraid I have another.
It was explained what vapour pressure was to us because we needed to know in relation to an experiment to do with a volatile liquid and I understood the phase equilibrium of vapour pressure but I asked if a liquid is considered volatile (readily turns to a gas) if it has a high or low vapour pressure relative to atmospheric pressure. The response was a liquid is volatile if it has a high vapour pressure.

But would it not be volatile if it has a low vapour pressure? -> The lower the pressure the easier it is for the molecules to diffuse away from each other and become a gas.

Sorry to keep this thread running way past the initial question but its what I'm on at the moment and I like to have it confirmed.

[Borek]

Volatile means "quickly evaporating and drying out". Liquid with a higher vapor pressure dries out faster, as it is easier for its molecules to become gaseous.

[MN1988]

sorry but that doesn't change my understanding of why this occurs.

Why do liquids with a high vapour pressure dry out faster?
like in the attached file there is some molecules turning to gas and some turning to liquid. if the rate of this happening is the same the it is said to reach the liquids vapour pressure.

But i don't get how pressure outside this system has an effect on this equilibrium (e.g. replace the container from a place of high pressure and put it in a room where it is subject to atmospheric pressure)

like if a jug of a volatile liquid is placed on the table and is subject to atmospheric pressure. then if atmospheric pressure is 1 atm and the vapour pressure of the liquid is say, 2 (I don't know the units as i really dont understand this) would it not be the case that atmospheric pressure is pushing down on the molecules causing them to come closer together. If the vapour pressure is lower, say 0.5 then those molecules could diffuse more relative to the atmospheric pressure pushing down on them and more would turn to a gas than condense to a liquid.

[Borek]

Why do liquids with a high vapour pressure dry out faster?

Higher vapor pressure means more molecules of the liquid in the air. More molecules in the air means more substance is in the air and less left as a liquid.

like in the attached file there is some molecules turning to gas and some turning to liquid. if the rate of this happening is the same the it is said to reach the liquids vapour pressure.

We are not necessarily talking about equilibrium.

But i don't get how pressure outside this system has an effect on this equilibrium (e.g. replace the container from a place of high pressure and put it in a room where it is subject to atmospheric pressure)

External pressure doesn't matter at all.

My bet is that you are making a common mistake of confusing the total pressure with the partial pressure of the vapor.

[MN1988]

Mixing up total pressure and partial pressures was it alright. Thanks for that I went off and learned the difference.
Thanks guys, you've been most helpful.