Question #4f833

1 Answer
Jun 8, 2017


Well, we have to make the distinction between condensed phases, solids and liquids, and non-condensed phases, gases...........


Gases are condensable materials. State functions can be derived that express density from pressure, temperature, and amount of gas variable........

#i.e.#, the #"Ideal Gas Equation"# #PV=nRT#:

#n/V=P/(RT)=("mass"/"molar mass")/V=P/(RT)#.....and thus

#"mass"/V=rho_"gas"=(Pxx"molar mass")/(RxxT)#.

And thus gaseous density is proportional to pressure, and inversely proportional to temperature.

On the other hand, while the expression for density is the same when we deal with solutions in the liquid or solid state, volume is relatively constant:

#rho="Mass"/"Volume"#. The volume of a liquid solution when we dissolve a mass of solute varies only (VERY!) marginally with respect to the pure solvent. When we stir sugar into a cup of tea or coffee, we are MANIFESTLY increasing solution density by adding mass, and yet the volume change upon dissolution would be very trifling, if we could measure it at all.

And thus with respect to pure water, and aqueous solution of some salt is DENSER than that of pure water. And we know this practically from the fact that you are certainly more buoyant in the ocean than in a fresh water pool.