Is the molar volume a physical or chemical property?

1 Answer
Jun 26, 2016

Well, since you can observe it without changing the composition or form of the matter, it's a physical property.

(In fact, if you do change the form of the matter, the molar volume changes, so that further demonstrates its physical nature.)


Molar volume is sometimes labeled #barV = V/n#, where #V# is the volume in #"L"# and #n# is the #"mol"#s of substance. It is the volume occupied by #"1 mol"# of the substance.

As long as you can measure the volume, and you know the mass and what substance you're looking at (so you can use its molar mass in #"g/mol"#), you can find the #"mol"#s, which allows you to find the molar volume.

EXAMPLE

If you have a volume of #"116 mL"# of ethanol (#"EtOH"#), and you acquire its mass as #"92.136 g"#, then convert to #"mol"#s and you have a pure molar volume of:

#color(blue)(barV_"EtOH"^"*") = "0.116 L"/(92.136 cancel"g") xx (46.068 cancel"g")/"mol"#

#=# #"0.058 L/mol"#

#=# #color(blue)("58.0 mL/mol")#

(Do keep in mind that a real liquid would have a different pure molar volume than a partial molar volume in a mixture, if we didn't assume volumes were additive.)