STP — Science definition
Standard Temperature and Pressure: 0°C (273 K) and 1 atm, the reference conditions for comparing gases.
Where it is taught
- The Ideal Gas Law — States of Matter & Gases, Physical Science: Chemistry, Grade 11
In use
Some standard-condition conventions instead use 100 kPa, giving a different value, so always state pressure and temperature rather than rely on the initials STP alone.
The Ideal Gas Law
Questions using stp
Problem 1
What volume does 3.0 mol of an ideal gas occupy at STP?
Answer and explanation
67.2 L
Volume = moles × 22.4 L/mol = 3.0 × 22.4 = 67.2 L.
Problem 2
How many moles of gas are present in a 11.2 L sample at STP?
Answer and explanation
0.5 mol
Moles = volume ÷ 22.4 L/mol = 11.2 ÷ 22.4 = 0.50 mol.
Problem 3
Explain why 1 mole of oxygen gas and 1 mole of helium gas occupy the same volume at STP, even though oxygen molecules are much heavier.
Answer and explanation
By Avogadro's Law, equal volumes at the same temperature and pressure hold equal numbers of particles, regardless of their mass. The ideal gas law depends only on the number of moles (n), not the type or weight of the gas, so one mole of any ideal gas fills 22.4 L at STP.
Problem 4
What volume does 2.0 mol of an ideal gas occupy at STP?
Answer and explanation
44.8 L
Volume = moles × 22.4 L/mol = 2.0 × 22.4 = 44.8 L.