Avogadro’s lawAvogadro’s law

Avogadro’s lawAvogadro’s law

Joseph Louis Gay-Lussac of France studied the

volume relationship of reacting gases.

In 1809, he published his results. He summarized

in a statement known as GAY-LUSSAC’S LAW OF

COMBINING VOLUMES OF GASES: When measured

at the same temperature and pressure, the ratios

of the volumes of reacting gases are the small

whole numbers.

Avogadro’s lawAvogadro’s law

H2 + Cl2 2 HCl

1 volume 1 volume 2 volumes

1 molecule 1 molecule 2 molecules

1 mol 1 mol 2 mol

Avogadro’s lawAvogadro’s law

AVOGADRO’S LAW states that equal volumes of

different gases at the same temperature and

pressure contain the same number of molecules.

If the amount of gas in a container is increased, the

volume is increased.

If the amount of gas in a container is decreased,

the volume is decreased.

Avogadro’s lawAvogadro’s law

As you increase the

amount of gas (i.e.

through inhalation) the

volume of the balloon

increases likewise.

Avogadro’s lawAvogadro’s law

This law was a real breakthrough in understanding the

nature of gases.

1. It offered a rational explanation of Gay-Lussac’s law

of combining volumes of gases and indicated the

diatomic nature of elemental gases, such as hydrogen,

chlorine and oxygen.

Avogadro’s lawAvogadro’s law

2. It provided a method for determining the

molecular weights of gases of known molecular

weight.

3. It afforded a firm foundation for the development

of the kinetic molecular theory.

Avogadro’s lawAvogadro’s law

The mathematical form of Avogadro’s law is:

V ; V1 = V2

n n1 n2

Sample problem 1

A sample of gas with a volume of 9.20 L is known to contain 1.225 mol.

If the amount of gas is increased to 2.85 mol, what new volume will

result if the pressure and temperature remain constant?

Avogadro’s lawAvogadro’s law

Solution

Given: V1 = 9.20 L V2 = ?

n1 = 1.225 mol n2 = 2.85 mol

Solution:

V2 = n2V1 = (2.85 mol) (9.20 L) = 21.4 L

n1 (1.225 mol)

Avogadro’s lawAvogadro’s law

Sample exercises

1. If 0.25 mol of argon gas occupies a volume of 7.62

mL at a particular temperature and pressure, what

volume would 0.43 mol of argon have under the

same conditions?

Avogadro’s lawAvogadro’s law

Sample exercises

2. At a certain temperature and pressure, a balloon with

10.0 g of oxygen has a volume of 7.00 L. What is

the volume after 5.00 g of oxygen is added to the

balloon?

The EndThe End

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