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Chapter 5: Gas Laws

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  1. The Ideal Gas Law
    1. Variables:
      V=volume (liters, cubic decimeters, milliliters, cubic centimeters).
      n=amount in moles, n = g / MM (MM = molar mass from Periodic Table).
      T=temperature, for gases must be in Kelvin, K = oC = 273.15, usually find temperature to nearest degree, so only add 273.
      P=pressure (atmospheres, millimeters of mercury, kilopascals, torr. 1 atm = 760 mm Hg = 101.3 kPa = 760 torr = 29.92 in Hg = 14.7 lb/in2, these are all at 0 oC

      torr named after Torricelli - Italian scientist, first person to accurately measure atmospheric pressure, 1640

      Calculation of Gas Pressure

      1. barometer - closed manometer, take  delta h directly.
      2. manometer - open manometer.
        Pgas = Patm + P due to  delta h mm Hg
      H2O is on the atmospheric side in the  delta h part of the equation, this will effectively give the addition or subtraction from atmospheric pressure.

      Relation between variables;

      PV=nRT

      where R is a true constant, it is the same for all gases and is independent of P, V, n or T.
      R = .0821 (L*atm) / (mol*K) = 8.31 (L*KPa) / (mol*K) = 8.31 J/ (mol*K) = 62.4 (mm Hg*L) / (mol*K)

      R = (PV) / (nT) inputting standard temperature and pressure (STP) for any gas will give the same R, Avogadro's Law - the same number of particles at the same P, T, and V.


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