Constant C in Vapor Pressure Equation

[pzona]

I'm working on vapor pressure for my general chemistry class, and I recently came across the curve P=C^(-[tex]\Delta[/tex]H/RT). I was wondering what the units are for C (or are there no units because it is a constant?) and where I could find a table of values for common liquids (water, ethanol, methanol, diethyl ether, etc.). I know that I can cancel out C when actually doing problems, but I was curious to see the magnitudes of the values and how much they differ from each other. I haven't been able to find a table of values so far, so if anyone has a link I'd appreciate it.

 

[Mapes]

The complete expression is

[tex]P=P_0\exp\left(\frac{\Delta S}{R}-\frac{\Delta H}{RT}\right)=P_0\exp\left(\frac{\Delta S}{R}\right)\exp\left(\frac{-\Delta H}{RT}\right)[/tex]

where [itex]P_0[/itex] is the unit pressure (e.g., 1 Pa, 1 bar, 1 atm, etc.) and [itex]\Delta S[/itex] is the entropy increase when the condensed phase evaporates. This equation is derived by setting equal the chemical potentials of the condensed and vapor phases.

 

[quicknote]

Hello,

Thank you for your question about the constant C in the vapor pressure equation. The constant C does not have any units because it is a dimensionless quantity. It is a constant that is specific to the substance being studied and takes into account the molecular interactions and size of the molecules.

As for a table of values for common liquids, there are various resources available online that provide this information. One reliable source is the NIST Chemistry WebBook (https://webbook.nist.gov/chemistry/), which has a database of thermodynamic and physical properties for a wide range of substances, including those you mentioned (water, ethanol, methanol, diethyl ether, etc.). You can search for a specific substance and find its vapor pressure at different temperatures.

I hope this helps with your research. Good luck with your studies!

Best,