Avogadro’s lawIdeal gases and molar volume

Elements that exist as gases at 25 °C and 1 atmosphere

• Gases assume the volume and shape of their containers.

• Gases are the most compressible state of matter.

• Gases will mix evenly and completely when confined to the same container.

• Gases have much lower densities than liquids and solids.

Physical Characteristics of Gases

Avogadro’s Law

1 mol H2 at STP = 22.4 L 1 mol O2 at STP = 22.4 L

STP stands for standard temperature & pressure

(0°C and 1 atm)

Avogadro’s Law

equal volumes of gases at the same temperature and pressure contain equal numbers of molecules.

Constant temperatureConstant pressure

Molar Volume of GasesThe volume occupied by one mole of a

gas at STP is known as the standard molar volume of a gas. It has been found to be 22.4 L.

1 mol = 22.4 L will be the conversion factor used in Avogadro’s law.

Sample Problem 1

A chemical reaction produces 0.0680 mol of oxygen gas. What volume in liters is occupied by this gas sample at STP?

Using our conversion factor of 1 mol = 22.4 L to solve for volume

1 mol

0.0680 mol x 22.4 L = 1.52 L O2

Sample Problem 2

A chemical reaction produced 0.098 L of sulfur dioxide gas, SO2, at STP. What was the mass (in grams) of the gas produced?

Sample Problem 2

First find molar mass of SO2:

1 x S = 32.07 g/mol

2 x O = 16 x 2 = 32 g/mol

64.07 g/mol

1 mol SO222.4 L

0.098 L x 1 mol SO2 x 64.07 g = 0.28 g