Can I use Boyle's law for a situation where the mass of the particles is held constant within a closed container and no chemical change occurs to these particles?

1 Answer
Truong-Son N.
Oct 20, 2016

Yes, the point is that the quantity of gas is fixed. Since you can convert between mass and #"mol"#s using the molar mass, it doesn't matter which one is held fixed; the other is held fixed by implication of the converted units.

The ideal gas law has three common formulations:

#PV = nRT#
#PVM_m = mRT#
#PM_m = DRT#

where:

  • #P# is pressure in, say, #"atm"# or #"bar"#.
  • #V# is volume in #"L"#.
  • #n# is the #"mol"#s of gas.
  • #M_m# is the molar mass of the gas in #"g/mol"#.
  • #D# is the density in #"g/L"#.
  • #m# is the mass in #"g"#.
  • #R# is the universal gas constant. If it is units of #"L"cdot"atm/mol"cdot"K"#, then pressure is in #"atm"#. If it is in units of #"L"cdot"bar/mol"cdot"K"#, then pressure is in units of #"bar"#. And so on.
  • #T# is the temperature in #"K"#.

You can interconvert between these.

#M_m * PV = M_m * nRT#

#=> color(blue)(PVM_m = mRT)#

#PVM_m * 1/V = m/VRT#

#=> color(blue)(PM_m = DRT)#

And furthermore, Boyle's law derives from the ideal gas law, so when the ideal gas law can use masses or #"mol"#s or density, Boyle's law holds true as long as if any of those are constant, in addition to the temperature.

#P_1V_1 = nRT#
#P_2V_2 = nRT#

#=> color(blue)(P_1V_1 = P_2V_2)#,
Boyle's Law

Related questions
See all questions in Boyle's Law
Impact of this question
1663 views around the world
You can reuse this answer
Creative Commons License