Standard Ambient Temperature and Pressure
Definition and meaning of Standard Ambient Temperature and Pressure in chemistry.
Standard Ambient Temperature and Pressure is a globally recognized reference state defined by a temperature of 298.15 K (25 degrees Celsius) and an absolute pressure of exactly 1 bar (100 kPa).
In more detail
This rigorous standard is used by scientists to uniformly report thermodynamic properties and chemical data under more typical, real-world laboratory conditions. Using this standard allows chemists worldwide to compare experimental results on a consistent basis without worrying about local environmental fluctuations. It differs significantly from the older Standard Temperature and Pressure convention, which utilizes a much colder temperature of 0 degrees Celsius. Because it aligns much closer to standard room temperature, it is often preferred when studying biological systems or reporting the enthalpy and entropy of spontaneous reactions.
Key facts
| Field | General Chemistry |
|---|---|
| Standard Temperature | 25 degrees Celsius (298.15 K) |
| Standard Pressure | 1 bar (100 kPa) |
| Ideal Gas Volume | 24.79 L/mol |
The standard enthalpy of formation for pure liquid water, widely reported in thermodynamic tables as -285.8 kJ/mol, is precisely measured at Standard Ambient Temperature and Pressure.
Frequently asked questions
How does this standard differ from STP?
It uses a warmer temperature of 25 degrees Celsius and exactly 1 bar of pressure, whereas STP conventionally uses 0 degrees Celsius and 1 atm of pressure.