Avogadro’s law

Definition

Avogadro's law states that the volume of a gas is directly proportional to the number of moles of gas when temperature and pressure are held constant. Mathematically, it can be expressed as $V \propto n$ or $\frac{V}{n} = k$.

5 Must Know Facts For Your Next Test

1. Avogadro's law explains the relationship between volume and amount (moles) of a gas.
2. The law implies that equal volumes of all gases, at the same temperature and pressure, contain an equal number of molecules.
3. It can be expressed with the equation $V_1 / n_1 = V_2 / n_2$ for two different states of a gas.
4. The concept is crucial for understanding molar volume, which is 22.4 L at standard temperature and pressure (STP).
5. Avogadro's number (6.022 x $10^{23}$) is derived from Avogadro’s hypothesis about equal volumes containing equal numbers of molecules.

Review Questions

• Explain how Avogadro's law relates the volume and amount of gas under constant temperature and pressure.
• Use Avogadro's law to calculate the new volume if the amount of gas changes from 2 moles to 4 moles while maintaining constant temperature and pressure.
• What does Avogadro’s law imply about the volumes of different gases under identical conditions?

Related terms

Ideal Gas Law:

A fundamental equation that describes the state of an ideal gas using pressure (P), volume (V), temperature (T), and amount in moles (n): $PV = nRT$.

Boyle’s Law: States that the pressure of a given mass of gas is inversely proportional to its volume at constant temperature: $P \propto \frac{1}{V}$ or $PV = k$.

Charles’s Law: Describes how gases tend to expand when heated; at constant pressure, the volume of a gas is directly proportional to its absolute temperature: $V \propto T$ or $\frac{V}{T} = k$.