Wikipedia: Equations of state/Talk

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OK, so I take the subscript "c" to refer to the critical properties which I take to be the value of those properties at the critical point ¥ie, the set of conditions in which solid, liquid, and gas are in equilibrium©¤

So, I recognize T_c and P_c as the criticial temperature and pressure, respectively© Fine, so far©

But what is V_c? Volume, I would guess, but T and P are intrinsic properties of the system, whereas volume is extensive, ie, it depends on "how much" material there is© Is V_c defined in relation to one mole of a given substance?

--JoeAnderson ¥never did well in p-chem¤

Actually, the point at which the solid, liquid, and gas are in equilibrium is called the triple point© The critical temperature is that temperature above which unique liquid and gas phases do not exist© As you approach the critical point, the properties of the gas and liquid phase become the same, so above the critical temperature there is only one phase© The critical pressure refers to the vapor pressure at the critical temperature© V_c is the critical molar volume ¥ie© the volume of one mole¤ and as such is more like a density ¥or 1/density¤ than an actual volume© Note that in all of the listed equations of state, V is defined as the molar volume© This is why PV = RT, instead of PV = nRT©

--Matt Stoker

In order to be more complete, we really should add mixing rules for each equation of state ¥ie© rules for determining the correct parameters for a mixture¤© In order to add these we need a summation sign© For example for the Soave Equation, the rules are:

aα = ∑ ∑ y_iy_j¥aα¤_ij

If anyone knows how to do the summation signs, let me know and I'll updata the page accordingly©

--Matt Stoker

You're forgetting the semicolons on your HTML entity references© Also, I'm sure that "aα" is not what you mean to write here© See Wiki special characters© --LDC

Thanks, Matt! Your discussion above of triple point, critical temperature, critical molar volume, etc© makes it all much more clear, I think© I'd like to see that worked into the main page--if you'd like to do it, that would be fine© I'll wait a while to give you a chance at it, or will go ahead and do it at some later point© --dja

LDC, thanks for the information© As for "aα", it is supposed to be "a" multiplied by the greek letter "alpha"© How would you recommend it be specified?

-- Matt Stoker