Pascal
Definition and meaning of Pascal in chemistry.
Pascal is the SI unit of pressure, stress, and Young's modulus. One pascal equals one newton of force applied evenly over an area of one square meter. It is named after the French scientist Blaise Pascal, who studied fluid pressure in the 1600s.
In more detail
A single pascal is a very small amount of pressure, so chemists and atmospheric scientists usually report measurements in kilopascals or megapascals instead. Standard atmospheric pressure at sea level equals exactly 101.325 kilopascals, or 101,325 pascals. In strict SI usage, the pascal has replaced older pressure units like the atmosphere and the torr, though those older units still appear often in traditional laboratory settings and older textbooks.
Using pascals consistently is important in thermodynamic calculations, since equations relating pressure, volume, and temperature require a single, standard unit system to give correct results. In base SI units, one pascal equals one kilogram per meter per second squared. This unit appears directly in the ideal gas law, PV = nRT, whenever pressure must be expressed in pascals to match the other units in the equation.
The pascal is a derived unit, meaning it is built from the more basic SI units of mass, length, and time rather than defined independently. The unit is also used outside chemistry, appearing in engineering fields to describe material stress and in meteorology to describe barometric pressure readings.
Key facts
| Field | Physical Chemistry |
|---|---|
| Unit symbol | Pa |
| Base units | kg / (m·s²) |
| Named after | Blaise Pascal |
| Standard atmosphere | 101,325 Pa (101.325 kPa) |
Standard atmospheric pressure at sea level is approximately 101,325 pascals, or about 101.3 kilopascals. A car tire, by comparison, is typically inflated to around 220,000 to 250,000 pascals of gauge pressure, well above normal atmospheric pressure. Deep-sea pressure increases quickly with depth. At 100 meters underwater, the surrounding pressure reaches roughly 1,100,000 pascals, more than ten times the pressure at sea level. Blood pressure, though usually reported in millimeters of mercury, can also be expressed in kilopascals in SI-based clinical settings.
Frequently asked questions
How many pascals are in one atmosphere?
There are exactly 101,325 pascals in one standard atmosphere (atm).
Why is the pascal a derived unit?
Because it is calculated from the more basic SI units of mass, length, and time, rather than being defined on its own.
Where is the pascal used in chemistry calculations?
The pascal appears in the ideal gas law and other thermodynamic equations whenever pressure must be expressed in standard SI units for the math to work out correctly.