Standard Temperature and Pressure
Definition and meaning of Standard Temperature and Pressure in chemistry.
Standard temperature and pressure (STP) is a reference state used in chemistry to enable consistent comparison of gas behavior and volumes. It is defined as 0°C (273.15 K) and 100 kPa pressure by current IUPAC standards, though older references use 1 atm (101.325 kPa) instead.
In more detail
Scientists need a standard reference point to compare gas volumes because gas volume depends strongly on both temperature and pressure. By defining conditions as STP, chemists can calculate or predict gas behavior consistently across different experiments and textbooks. At IUPAC STP (100 kPa), one mole of an ideal gas occupies approximately 22.7 liters; at the older standard (1 atm), one mole occupies 22.4 liters. This distinction is crucial in gas stoichiometry calculations.
Key facts
| Temperature | 0°C (273.15 K) |
|---|---|
| Pressure | 100 kPa (IUPAC standard); 1 atm (101.325 kPa) in older definitions |
| Molar Volume (Ideal Gas) | Approximately 22.7 L per mole |
| Field | Physical Chemistry |
If you have 2 moles of nitrogen gas (N2) at STP, its volume would be approximately 45.4 liters using the IUPAC definition (22.7 L/mol × 2 mol).
Frequently asked questions
Why is there confusion about STP definitions?
IUPAC changed the standard pressure from 1 atm (101.325 kPa) to 100 kPa in 1982. Older textbooks still reference the 1 atm definition, which produces a molar volume of 22.4 L instead of 22.7 L.
How do I use STP in chemistry problems?
Use the molar volume (22.7 or 22.4 L/mol depending on which standard) to convert between moles and liters of gas, or apply the ideal gas law with T = 273.15 K and P = 100 kPa.