Avogadro's Law

QuickNotes

Avogadro's Law: (V1/n1) = (V2/n2)

• n = moles of gas  
• V = volume 
• The same units must always be used on both sides of the equations

(8 L)/(10 mol) = (4 L)/(5 mol)

(8 mL)/(10 mol) = (4 L)/(5 mmol) 

• Important Concept: At a constant temperature and pressure, volume and moles of gas are directly proportional. This means that as the moles of gas increase, the gas's volume increases, and vice versa.
• Because there is no realistic version of an ideal gas, gases that obey this law are generally found to be at low pressures.

Example:

If a 15.7 L sample of O2 with 0.700 mol of gas at a temperature of 273 K and 1 atm is converted to O3 at the same pressure and temperature, what is the new volume of O3?

1. Set up a balanced chemical equation:

3O2  --> 2O3

2. Use the equation to determine the number of moles of O3 yielded by 0.70 mol of O2 

(0.700 mol O2) (2 mol O3/ 3 mol O2) = 0.467 mol O3

3. Substitute known values into Avogadro's law to obtain the volume of O3

(15.7 L O2)/(0.700 mol O2) = (? L O3)/(0.467 mol O3)

V = 10.5 L O3

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