Ideal gases must satisfy two conditions: the gas particles must occupy negligible volume relative to the container volume, and there must be no attractive or repulsive forces between gas particles. At high pressure, the volume between particles (the "free volume") is actually much less than the container volume. Equally important, when gases are subjected to high pressure, the particles can be close enough to interact.
The Dutch physicist Johannes van der Waals developed an equation to correct for the non-ideal behavior of gases. It's based on the ideal gas law and includes a factor that adjusts P upward to compensate for the decrease in P due to intermolecular attractions in real gases. The van der Waals equation also includes a factor that adjusts V downward, to give a measure of only the free volume in the container by excluding the volume occupied by gas particles. The van der Waals equation is:
The a and b terms are called the van der Waals constants and depend on the identity of the gas. For hydrogen gas, the van der Waals constants are:
Imagine that you have a 1.00 mole sample of hydrogen gas in a 1.00 L container at 0.00
C. Discuss whether you believe hydrogen gas is an ideal gas under these conditions. How do you decide? If you believe the gas is not ideal under these conditions, under what conditions of P, V, or T would the gas behave ideally? And what criteria do you use to decide? Explain your reasoning to your classmates, and respond to their explanations.
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Andrew Park
ReplyDeleteOkay, so I don't really fully understand this section so I might be wrong. If I am, you can point it out and I guess I'll have to read over other people's comments to understand this.
Anyway, with constant a being .244 and constant b being .0266, I believe that the sample of hydrogen gas is not an ideal gas under these conditions. This is because an ideal gas has values that are around STP(Standard Temperature and Pressure). STP values are when temperature is at 0 degrees celsius and pressure is at 1 atm. However, in this problem, pressure is at about 23 atm, although the temperature is at 0 degrees celsius. Thus, at the conditions of pressure being 1 atm, temperature at 0 degrees celsius, and a volume that is low would the gas behave ideally. The ideal gas law revolves around these concepts.
Megan Dickson
ReplyDeleteI believe that the hydrogen gas presented here with an a value of 0.244 and a b value of 0.0266 does act as an "ideal gas." When you use van der Waal's equation to find the pressure of the hydrogen gas identified, you find that the pressure is about 22.76 atm. This pressure is relatively low. Ideal gases must be under conditions of relatively low pressures and high temperatures. If hydrogen were at a higher pressure, then the gas molecules would be pushed closer together and the volume of the gas molecules would become significant. I think that 0 degrees celcius, or 273 degrees kelvins is not a low temperature, so the molecules are still in constant movement at this temperature and in random motion.
Thus, at these conditions I think that the hydrogen gas sample follows the premises that make up an ideal gas. If my reasoning is flawed, let me know. I was not entirely certain about some of the ideas presented in the lesson about ideal gases.
Megan Dickson
ReplyDeleteAndy, I think that you used van der Waal's equation correctly, but I think that you might not be right about ideal gases. In order to act as an "ideal gas" I do not think that gases need to be at standard temperature and pressure. I think that an ideal gas must be at a relatively high temperature so that its particles are in constant, random motion. An ideal gas must also be at a relatively low pressure so that the particles have room to move around freely and so that they are not contrained and thus have a measurable mass.
using a, b and van der Waals equation gives the lower atmosphere that the original equation PV=nRT. This tells that the hydrgen is the ideal gas. If hydrgen had high pressure than the volume will be increased, high temperature will make increase in pressure, and high volume means the lower pressure. To make the hydrogen gas to be fit on PV=nRT, the n, which is the moles, should increase or the V, the volume should increase in the equation of vad der Waals'.
ReplyDeleteDwayne Hahm
Thank you, Megan an Andrew. I wasn't sure about this disscusion, but now I got it little bit, I guess. Defining the gas to be ideal or not was hard question for me and now I understand how to get it.
ReplyDeleteDwayne Hahm
Ellen Cho
ReplyDeleteI think hydrogen gas is not an ideal gas. It said that there must be no attractive or repulsive forces between gas particles to be an ideal gas. However, with with an a value of 0.244 and a b value of 0.0266, it's about 23 atm. Since the hydrogen gas has some pressure on it, it may have some attractive or repulsive forces. Even though the attractiveness is not a lot, it fails to satisfy one of ideal gas that the hydrogen gas is not an ideal gas.
Ellen Cho
ReplyDeleteI didn't really understand what the ideal gas. Now I know that the ideal gas should have low pressure and high temperatures. However, I also agree that the ideal gas should have STP values since it should have no attractive or repulsive forces.
An Ideal gas is a gas described as having a low pressure and plenty of room for the particles to move around. Using the constants of a and b in the van der Waals equation of:
ReplyDelete(P + n^2a/V^2)(V-nb)=nRT.
As stated before, at STP you find Megan's answor, around 22.76 atm.
An ideal gas is stated to have an extremely low pressurea and compared to most other substances, this is a very low pressure which would insist on this being an Idea gas.
Allie VanO
Thank you Megan for your first answer, it did help me with understanding this chapter a little better than I originally had.
ReplyDeleteThis chapter was rather difficult so for anyone feeling a bit confused don't feel down about it.
Getting down all the different laws and equations and memorizing which goes to which is not necessarilly the easiest thing in the world to do. So congrats on getting this far!
Allie Vano
Josh Dos Santos
ReplyDeleteSorry!!! I forgot about this since it wasn't up on Friday :(
Anyways...
Here is my reasoning...
0 degrees celsius is not very high so check. This is ideal.
Moreover, the constants that are used to compensate for non-ideal behavior and adjust the equation are relatively small (a=.244 and b=.0266). Since the change is small,
Hydrogen behaves very close to ideally.
Thus, it is ideal. :)
Josh Dos Santos
ReplyDeleteAndy, I think I can point out the mistake in your reasoning.
If I am not wrong myself, an ideal gas requires relatively low pressure. This is why you automatically think STP. However, low pressure does not necessarily occur at 0 degrees Celsius. It depends of the amount of gas and the volume as well.
Hope that makes sense. :)
Josh Dos Santos
ReplyDeleteWell, I got 22.94 atm pressure using the van der waals equation.
Now, here is my newly realized problem:
Hydrogen is a very ideal gas. IT is at an ideal temperature. However,
Isn't 22.94 atm high??? Considering normal atm is 1??
I thought that in order to discuss this problem we actually had to solve the equations with real values. And i think that hydrogen is a ideal gas, even though there is a slight difference in the value that i obtained.
ReplyDeleteSo, First off, we will find the pressure of the hydrogen gas in the Van der Waal equation. When we plug all the numbers in there, it will look like:
(p+0.244/1)(1-0.0266)=(0.08206)(273)(1)
Now, we just need to solve the equation for the p, which looks like:
(p+0.244)(0.9734)=(22.40238)
0.9734p+0.2375096= 22.40238
0.9734p = 22.1648704
p = 22.77056
So using van der waal equation, we get the atm of the hydrogen gas as 22.77 atm.
Now, for the comparison, we will use the ideal gas law for the hydrogen gas.
P=(nRT/V)
P= (1*273*0.08206)/1
p= 22.40 atm
The two values that were obtained from two different equation is surprisingly similar in their values. And i think this similarity in the values show that the hydrogen in this condition is an ideal gas.
*the reasoning for this idea was based on the equation and actual mathematical values that i have obtained. I'm just saying because it asked how do i decide.....
Josh, i think that the pressure that we obtained shouldn't be related to 1 atm. Like you have said to andrew, 1 atm is just standard pressure that we use. If you use the ideal gas equation with these values, you will also get 22.4 atm.
ReplyDeleteThe thing that now i am concerned with is that isn't our values to big.... Like you have said, the values that we obtained from van der waal equation is very close to the ideal gas value. However, if we change these values into torrs, or mmHg, now we see that there is actually big difference in the value. In atm value wise, it is very similar, but in torr or mmHg value wise, it shows big difference. To what extent should we decide that the value is close enough to each other?