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### Topic: Gas Laws and volume  (Read 7356 times)

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#### Needaask

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« Reply #15 on: April 29, 2013, 11:16:49 PM »
I'm not sure what your question is.  These are just different ways of measuring concentration.  (v/v, w/w etc.)

Oh sorry about that. What I didn't understand was what they meant by 21% oxygen by volume. Would the by volume mean v/v or w/v?

#### Corribus

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« Reply #16 on: April 29, 2013, 11:54:20 PM »
volume to volume, but since the gas is ideal and volumes are additive, it's equivalent to mole fraction.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

#### Needaask

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« Reply #17 on: April 30, 2013, 06:43:02 AM »
volume to volume, but since the gas is ideal and volumes are additive, it's equivalent to mole fraction.

In the v/v formula it is volume of solute over volume of solution times hundred percent. So what would the volume of solute and of solution be in this equation?

Also for the Amagat's Law and additive volumes, the law requires the temperature and pressure to be a constant. What does that mean? Does it mean each gas must have an equal pressure?

Thanks for the help #### Corribus

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« Reply #18 on: April 30, 2013, 05:06:50 PM »
In the v/v formula it is volume of solute over volume of solution times hundred percent. So what would the volume of solute and of solution be in this equation?
It's just a volume fraction - volume of the gas divided by total volume of the mixture.

Quote
Also for the Amagat's Law and additive volumes, the law requires the temperature and pressure to be a constant. What does that mean? Does it mean each gas must have an equal pressure?
One way to read it might be that the pressure of the overall mixture doesn't change after mixing due to non-idealistic behavior.  I.e., if you mix two gasses and the overall pressure (and temperature) doesn't change, then the volumes are exactly additive.  See Borek's example above about a removable membrane to help explain this.

Amagat's law and Dalton's law are equivalent for ideal-gasses - they are erroneous for different reasons when it comes to real gasses.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

#### Needaask

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• Mole Snacks: +6/-16 ##### Re: Gas Laws and volume
« Reply #19 on: April 30, 2013, 11:36:54 PM »
In the v/v formula it is volume of solute over volume of solution times hundred percent. So what would the volume of solute and of solution be in this equation?
It's just a volume fraction - volume of the gas divided by total volume of the mixture.

Quote
Also for the Amagat's Law and additive volumes, the law requires the temperature and pressure to be a constant. What does that mean? Does it mean each gas must have an equal pressure?
One way to read it might be that the pressure of the overall mixture doesn't change after mixing due to non-idealistic behavior.  I.e., if you mix two gasses and the overall pressure (and temperature) doesn't change, then the volumes are exactly additive.  See Borek's example above about a removable membrane to help explain this.

Amagat's law and Dalton's law are equivalent for ideal-gasses - they are erroneous for different reasons when it comes to real gasses.

Oh so it's like partial volume/total volume of container times 100%?

Also, after reading Borek's example, actually what would the reason for the volume to be additive in this case? Besides their total pressure individually would add up to the mixture's pressure and temperature be constant?

And why would the partial volume/total volume be equal to the mole fraction?

Thanks for the help #### Corribus

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« Reply #20 on: May 01, 2013, 10:25:56 AM »
And why would the partial volume/total volume be equal to the mole fraction?
Because it's based on the assumption that volume is an extensive property - i.e., proportional to the amount of stuff in the system.  By definition extensive properties are additive, assuming the system is noninteracting (i.e., gasses behave ideally).  If the volume of a substance is proportional to the amount of moles, then the the volume of each substance is proportional to the product of mole fraction of the substance and the total volume.

That is: V (substance) / V (total) = n (substance) / n (total)
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

#### dinagross

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« Reply #21 on: May 04, 2013, 05:55:45 AM »
The Ideal Gas Law is used to relate the pressure, volume, temperature and amount of an "ideal" gas. Although many gases are not perfectly ideal in reality, you can usually use the Ideal Gas Law anyway. Here is how you solve these problems!
The Ideal Gas Law is: PV = nRT.