Barometer
Definition and meaning of Barometer in chemistry.
A barometer is an instrument that measures atmospheric pressure and indicates changes in air pressure. Mercury barometers, invented by Evangelista Torricelli in 1643, have historically been among the most accurate types, though modern digital barometers can now match or exceed this accuracy.
In more detail
In a mercury barometer, atmospheric pressure pushes liquid mercury up a closed tube, with the height of the mercury column directly indicating pressure. Modern aneroid barometers use sealed metal chambers that expand or contract with pressure changes, requiring no liquid. Barometers are essential in chemistry labs because atmospheric pressure significantly affects gas volumes, boiling points, and reaction rates. Recording atmospheric pressure during experiments ensures results can be reproduced and compared under standard conditions.
Key facts
| Field | Physical Chemistry |
|---|---|
| Standard atmospheric pressure | 760 mmHg (millimeters of mercury) or 1 atm or 101.3 kPa |
| Primary liquid (traditional) | Mercury (Hg) |
| Modern alternative | Aneroid barometers use mechanical springs instead of liquid |
A mercury barometer on a typical day at sea level shows a mercury column height of approximately 760 mm (or 760 torr), representing one standard atmosphere of pressure. At high altitude, the same barometer would register only 630 mm, reflecting the lower atmospheric pressure.
Frequently asked questions
Why is atmospheric pressure important in chemistry?
Atmospheric pressure affects gas volumes (Boyle's law), boiling points, and reaction rates. Standard conditions (1 atm) are used as reference points for all chemical calculations and data reporting.
What is the difference between a barometer and a manometer?
A barometer measures absolute atmospheric pressure, while a manometer measures pressure differences between two points or gauge pressure relative to atmosphere.