Why Does the Ideal Gas Law Fail at the Critical Point of Carbon Tetrachloride?

[coolnessitself]

[SOLVED] ideal gas law numerically

If I calculate the pressure of water vapor at stp (in mmHg),
P= 1000*7.502e-3*R*(0+273)*.804/18;
where the 7.502e-3 factor converts from Pa to mmHg, 1000 is because my density (.804) is in grams/cm^3, 18 is the molar mass of water, etc etc. and this comes out to be 760mm (1atm), as expected. Now, here's the problem. I've got carbon tetrachloride at it's critical point. Literature shows its T_c = 283.15, density_c=.5576, and pressure_c = 34181 mmHg. However, if I just do
P= 1000*7.502e-3*R*(283.15+273)*.5576/154.01;
I get 125.6 mmHg, not 34181 mmHg. Where did I go wrong? Is it just that the dieal gas law fails, because I've also tried data points that aren't near the critical region and at room temp and neither work..

 

[learningphysics]

Is your density in g/cm^3 or g/L ?

 

[ogb p]

It seems like you have made a mistake in your calculation. The ideal gas law should work for any gas, including carbon tetrachloride at its critical point. However, you may need to use different units for the gas constant (R) depending on the units of your other variables. It is also important to make sure that all of your units are consistent throughout the calculation. I would recommend double-checking your calculations and making sure you are using the correct units for each variable. If you are still having trouble, please provide more information about your calculations so I can assist you further.