Avogadro's Law

  1. Some typical data from the lab you did exploring the relationship between moles and volume is shown below:
    Moles of Gas
    Volume (L)
    0
    0
    0.0089
    0.200
    0.0179
    0.400
    0.0268
    0.600
    0.0357
    0.800
    0.0446
    1.000
  2. Notice the simple relationship depicted by the graph. Is it directly proportional or inversely proportional? If you don't know look at our other examples.
  3. Let's derive Avogadro's Law:
    f(x) = B*x or
    y = constant*x or
    V= constant*n or
    V/n = constant so
    V1/n1 = V2/n2
  4. Two assumptions about the experimental conditions must be made for this relationship to be true. What are they? (What other factors can affect volume?)

  5. Unlike the other "constants" which were found during the discovery of Boyle's Law and Charles' Law, the constant found above holds true for all gasses under the same temperature and pressure conditions.
  6. Avogadro did many experiments in which he chemically combined various volumes of different gasses. They always combined in simple whole number ratios. This lead Avogadro to conclude that equal volumes of gasses under the same temperature and pressure conditions contain the same number of gas molecules. Even though he didn't know how to calculate moles his experiments verified the relationship we see above. Regardless of what gas is used, the same ratio of volume to moles is always found: 22.4 L/mol at standard temperature (0°C) and standard pressure (1 atm). This is known as the Standard Molar Volume of a gas - 22.4L at STP.

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