6.5 Molar Volume of a Gas at STP
Notes
At STP (standard temperature and pressure: 0 °C and 1 atm), 1 mol of any gas takes up 22.4 L. This is the molar volume.
- Moles to liters at STP: multiply by 22.4 L/mol. Liters to moles: divide by 22.4 L/mol.
- It does not matter which gas: 1 mol of $\text{H}_2$ and 1 mol of $\text{CO}_2$ both fill 22.4 L at STP.
- Example: 2.50 mol of $\text{O}_2$ at STP is $2.50 \times 22.4 = 56.0$ L.
- Gas density at STP $\displaystyle = \frac{\text{molar mass}}{22.4 \text{ L/mol}}$.
Practice
What volume does 0.500 mol of $\text{N}_2$ occupy at STP?
$0.500 \times 22.4 = 11.2$ L.
How many moles are in 67.2 L of He at STP?
$\displaystyle \frac{67.2}{22.4} = 3.00$ mol.
What is the density of $\text{CO}_2$ gas at STP? (molar mass 44.01 g/mol)
$\displaystyle \frac{44.01 \text{ g/mol}}{22.4 \text{ L/mol}} = 1.96$ g/L.
Ready for more? Take the Unit 6 test.