Dr. Collins Unit 5 Gases Question

[rb4hu]

Advertisement - Members don't see this ad

Hi,
For some odd reason, I cannot understand how to get the correct answer to the following problem:

In a fixed volume container, 6x10^23 molecules of a gas exert a pressure of 12n/m^2. If 12x10^23 molecules of gas were added to the container, what would the pressure become?

The correct answer is 36n/m^2 . Can anyone please tell me how this is the answer using the ideal gas law. Thanks!

 

[BadgerPharm]

Hi,
For some odd reason, I cannot understand how to get the correct answer to the following problem:

In a fixed volume container, 6x10^23 molecules of a gas exert a pressure of 12n/m^2. If 12x10^23 molecules of gas were added to the container, what would the pressure become?

The correct answer is 36n/m^2 . Can anyone please tell me how this is the answer using the ideal gas law. Thanks!

I don't think the ideal gas law is used here. Try using Avogadro's Law.

Thought about it twice, it's the ideal gas law rearranged based off of a result of Avogadro's Law which implies that all gases have the same ideal gas constant.

 

[rasouls]

Hi,
For some odd reason, I cannot understand how to get the correct answer to the following problem:

In a fixed volume container, 6x10^23 molecules of a gas exert a pressure of 12n/m^2. If 12x10^23 molecules of gas were added to the container, what would the pressure become?

The correct answer is 36n/m^2 . Can anyone please tell me how this is the answer using the ideal gas law. Thanks!

It should triple since ( 6 x 10 ^23 )+ (12 x 10^23) molecules = 18 x 10 ^23

so the number of molecules has triples.


You can use the PV=NRT, since V,R, T are all constant then P=N. If the initial pressure is 12 then it has to triple to 36 🙂

let me know if that makes sense

 

[rb4hu]

Oh wow! Thanks...I was reading the problem completely wrong but your explanation helps a lot! Thanks so much.

 

[dudecoolname]

Rasouls explained it perfectly. Usually you don't need to go through the whole PV=nRT thing as far as plugging in all the values. Just know that values on opposite sides of the equal sign are directly proportional, and values on the same side of the equal sign are inversely proportional.

In this case, the value for n triples so the value of P will triple as well.

Also, what probably slipped you up was that it says 12*10^23 molecules are added. So the total goes from 6*10^23 to 18*10^23

 

[JonPrePharmD]

Rasouls explained it perfectly. Usually you don't need to go through the whole PV=nRT thing as far as plugging in all the values. Just know that values on opposite sides of the equal sign are directly proportional, and values on the same side of the equal sign are inversely proportional.

In this case, the value for n triples so the value of P will triple as well.

Also, what probably slipped you up was that it says 12*10^23 molecules are added. So the total goes from 6*10^23 to 18*10^23

+1 👍

 

[jjingle]

Isn't it just
P1/n1 = P2/n2

Since we know P1 and n1 and that n2=3*n1, we can find P2.

 

[jackal head]

Hi,
For some odd reason, I cannot understand how to get the correct answer to the following problem:

In a fixed volume container, 6x10^23 molecules of a gas exert a pressure of 12n/m^2. If 12x10^23 molecules of gas were added to the container, what would the pressure become?

The correct answer is 36n/m^2 . Can anyone please tell me how this is the answer using the ideal gas law. Thanks!

ideal gas law aside, all I would think is since gas molecules triple, pressure must also triple.

 

[chemguy79]

ideal gas law aside, all I would think is since gas molecules triple, pressure must also triple.

Logical argument, but there are flaws in said logic.

If one doesn't know PV=nRT ... Who is to say that there wouldn't an indirect relationship between moles of gas and pressure. We KNOW that the moles of gas increases by a factor of 3, but someone could logically rationalize that it reduces by a factor of 3. Furthermore, if the equation were like KE = 1/2mv^2, it could increase by a factor of 9 or decrease by a factor of 9. (Now, we have 4 answer choices for a multiple choice exam, all of which are completely logical if you don't know the equation in question.)

Point being, given the question, we know that there is a relationship between the two variables. However, the equation is necessary to establish if there is a direct relationship or an inverse relationship between the two components.

 

[thesituation559]

I have a question on 5-3 of the packet in the gas law section. How do you do that problem i cant figure it out. The answer is 5 liters but how do you get that? thanks

 

[JonPrePharmD]

I have a question on 5-3 of the packet in the gas law section. How do you do that problem i cant figure it out. The answer is 5 liters but how do you get that? thanks

Volumes of different gasses at same T and P contain equal # of gas molecules. It says that directly below section C.

So 7.5 L of H2 reacts.

If 7.5 L = 3 moles H2, then 2 moles Ammonia = what?

If you can't see that it's 5 L right away, find out what 1 mole is equal to.
7.5L/3moles = 2.5 L

2 Moles Ammonia = 5 L