Questions on pressure and non-ideal gases

In summary, the conversation revolved around calculating the pressure and energy of a non-ideal gas, specifically water vapor. The use of a constant for the specific gas, as well as the ideal gas equation and van der Waals equation, were discussed. However, using an equation of state for a substance with hydrogen bonding, like water, may not yield accurate results. The NIST steam tables were recommended as a better source for calculating pressure and other properties of water.
  • #1
Bobcent
31
0
Hi!

I have two questions.

First, how do I calculate the pressure of a non-ideal gas if I know volume, temperature and the number of moles? The gas in question is water vapor. I suspect a constant for the specific gas will be involved. Which constant is this?

And secondly, how do I calculate how much energy is stored in a pressurized gas if I know the mass (or the number of moles) and the pressure of the gas?

Thanks in advance! :smile:
 
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  • #3
Nugatory said:
Googling for "non-ideal gas presure" brings up a bunch of links. Maybe start with
http://chemwiki.ucdavis.edu/Physical_Chemistry/Physical_Properties_of_Matter/Gases/Real_Gases ?

Thanks for your post, good explanation! The problem is that I don't seem to be getting the right answer.

Water vapor has a density of 0.6 kg/m3 at 100 degree celsius (373 degree kelvin) and standard atmospheric pressure.
Source: http://www.wolframalpha.com/input/?i=Water+vapor+density+at+atmospheric+pressure

So if I put in all the values for water vapor except pressure, I should get 1 atm as the answer, but instead I get approximately 0.032 atm.

These are the values I used:

P = Unknown
V = 1 Liter
a = 5.464 According to the website you linked
n = 0.6/1000/18 = 3.33*10^-5 moles
b = 0.0305 According to the website you linked
R = 0.08260 According to the website you linked
T = 373 Degree kelvin

Done the calculation several times, don't understand what's wrong...

Thankful for help!
 
  • #4
It's difficult to say what is wrong with your calculation if you don't show it.

But the corrections to the ideal gas equation for the given parameters are really small.
The ideal gas gives approximately 1 atm and so should the van der Waals equation.
There is an error in the equation on this site, I believe. It should not be P squared, it does not make sense (dimensionally).
 
  • #5
Using an equation of state for a substance with hydrogen bonding, especially water, is never going to give you a good answer. Regardless, I looked up the specific volume of saturated water vapor at 1atm and 373.15K using the NIST steam tables, which was .0332 mol/L and used the ideal gas law to find pressure: .082057*373.15*.0332=P=1.0166 atm. You could use the virial equation or compressibility factor, but why bother. Water has tabulated values, make use of em! http://webbook.nist.gov/chemistry/fluid/
 
Last edited:
  • #6
Thanks for the help everyone, got it right now! :)
 

1. What is pressure and how is it measured?

Pressure is the amount of force applied per unit area. It is typically measured in units of Pascals (Pa), which is equivalent to 1 Newton per square meter. Pressure can be measured using a variety of instruments such as barometers, manometers, or pressure gauges.

2. How does pressure affect the behavior of gases?

In gases, pressure is directly proportional to temperature and inversely proportional to volume, according to the ideal gas law. This means that an increase in pressure will result in an increase in temperature and a decrease in volume, and vice versa. In non-ideal gases, other factors such as intermolecular forces and molecular size can also affect the behavior under pressure.

3. What are the differences between ideal and non-ideal gases?

Ideal gases follow the ideal gas law, which assumes that the particles have no volume and there are no intermolecular forces between them. In reality, most gases deviate from this behavior and are considered non-ideal. Non-ideal gases have finite particle size and experience intermolecular forces, resulting in different behavior under pressure and temperature changes.

4. How does pressure affect the boiling point of a substance?

Pressure has a direct effect on the boiling point of a substance. When the pressure on a liquid is decreased, the boiling point also decreases, causing the liquid to boil at a lower temperature. This is why water boils at a lower temperature at higher altitudes where the atmospheric pressure is lower.

5. What are some real-life applications of pressure and non-ideal gases?

Pressure and non-ideal gases have many practical applications in our daily lives. For example, understanding pressure is crucial in scuba diving, as the increasing pressure with depth can affect the behavior of gases in our body. Non-ideal gases also play a role in the functioning of engines, refrigerators, and other industrial processes.

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