bar
Definition and meaning of bar in chemistry.
Bar is a unit of pressure equal to 100,000 pascals (Pa), used throughout chemistry to express the pressure of gases and liquids in laboratory and industrial contexts. It is a non-SI unit but widely accepted in scientific practice.
In more detail
One bar is approximately equivalent to standard atmospheric pressure at sea level (1 atm ≈ 1.01325 bar), making it convenient for laboratory applications. The unit is commonly used in thermodynamics, gas law calculations, and chemical equilibrium expressions. Because bar is close to atmospheric pressure, it provides an intuitive reference point for scientists working with gaseous systems. In phase diagrams and equilibrium calculations, pressures are frequently expressed in bars rather than pascals.
Key facts
| Field | Physical Chemistry |
|---|---|
| SI Equivalent | 100,000 pascals (100 kPa) |
| Atmospheric Pressure | 1 atm = 1.01325 bar |
| Symbol | bar |
When calculating the equilibrium constant Kp for the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), the partial pressures of gases are often expressed in bars, such as 50 bar for nitrogen in an industrial ammonia synthesis reactor.
Frequently asked questions
Why is bar used instead of pascals?
Bar is more practical for laboratory work because it approximates atmospheric pressure and yields intuitive values. Many instruments, databases, and legacy systems use bars, so it remains standard in chemistry.
Is bar an SI unit?
No, bar is non-SI, though it is recognized and accepted internationally. The SI unit of pressure is the pascal (Pa).