Shortcut Methods
Numerical : Shortcut and Trick
-1. Calculate the pressure exerted by 1 mole of an ideal gas at a temperature of 273 K and a volume of 22.4 L.
Remember that at STP (standard temperature and pressure), one mole of any gas occupies 22.4 L and exerts a pressure of 1 atm. So, the pressure in this case is simply 1 atm.
- 2. What is the molar mass of a gas that has a density of 1.9 g/L at STP?
Trick: Use the fact that at STP, the density of any ideal gas is equal to its molar mass in g/mol. So the molar mass of the gas is simply 1.9 g/mol.
- 3. A sample of gas has a volume of 10 L and a pressure of 2 atm. What will be the volume of the gas if the pressure is increased to 4 atm at the same temperature?
Shortcut: Use the inverse relationship between pressure and volume (Boyle’s Law). The volume will halve when the pressure doubles, so the new volume will be 5 L.
