Avogadro's Hypothesis and Law

Background:

Two equal volumes of gas, at the same temperature and pressure, contain the same number of molecules.

Avogadro's Law:

At a constant temperature and pressure, the volume of a gas is directly proportional to the number of moles of that gas.

Mathematically, this can be represented as:

Volume (V) = Constant (K) x Moles (n)

Avogadro's Interpretation of Joseph Guy-Lassac's Law:

The pressure and temperature of a gas, like the volume and temperature, are directly proportional (assuming volume remains constant).

Mathematically, this is:

P/T=K
so we can then make the equation:
P/T=P₁/T₁
to solve for unknowns.

Explanation and Discussion:

Avogadro's Interpretation of Guy-Lussac's observations is a law that creates a similar equation to Charles' Law. This lets pressure and temperature be solved for with an unknown or constant volume. This completes the third part of the Combined Gas Law.

Avogadro's Hypothesis and Law describe the relationship of moles of a gas to the volume of its container. When pressure and temperature remain constant, there is a direct relationship between the two. Experimentation has determined this to be about 22.4 L per each mole of a gas at STP. Here is an example of this, note that the volume stays the same but the mass varies:

Drawing of 3 Gas Collectors with
data. The gases are oxygen, argon, and nitrogen. Although the masses
vary (32, 40, and 28 g), the volumes all stay at 22.4 L (the
pressure and temperature are constant at 273K/1 atm)

Let's consider a real example of Avogadro's Law. Have you every inflated a balloon? Most likely, you either pumped air in our blew air in yourself. Did the balloon inflate totally as soon as you started? Probably not. If you didn't inflate the balloon enough, perhaps you have heard a comment that there was "not enough air" in the balloon. This is a direct observation from Avogadro's Law. The more air you would put into the balloon, the greater its volume would be, because the volume of the balloon is the volume of the trapped gas.

Continued Study
For continued study, you can visit our Avogadro's Law bonus page. You can also test yourself. You can also learn about Amedeo Avogadro.

Sources:

: Brown, Theodore L., H. Eugene LeMay, Jr. and Bruce E. Burston, Chemistry: The Central Science, Englewood Cliffs, NJ: Prentice Hall, Inc., 1994
: Dorin, Henry, Peter E. Demmin, and Dorothy L. Gabel. Prentice Hall Chemistry: The Study of Matter, Needham, Massachusetts and Englewood Cliffs, New Jersey: Prentice Hall, Inc., 1989.
: Roper, Gerald C., "gas laws" Groliers New Multimedia Encyclopedia, Release 6, 1993
: Kauffman, George B., "Avogadro, Amedeo" Groliers New Multimedia Encyclopedia, Release 6, 1993

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