Barometer
Definition and meaning of Barometer in chemistry.
A barometer is a scientific instrument that measures atmospheric pressure. It shows how the weight of the air changes over time. Mercury barometers were invented by Evangelista Torricelli in 1643. Modern digital barometers now measure pressure with even greater accuracy.
In more detail
Atmospheric pressure is the weight of the air pushing down on everything. A traditional mercury barometer measures this push using a closed glass tube. The tube sits upside down in a pool of liquid mercury.
The heavy air pushes down on the pool. This forces the liquid mercury up into the empty tube. The height of that liquid column directly shows the air pressure.
When pressure rises, the mercury climbs higher. When pressure drops, the liquid falls. Modern aneroid barometers do not use any dangerous liquid.
They use a sealed metal chamber instead. This chamber expands or shrinks as the outside air pressure changes. Mechanical springs measure these tiny movements.
Barometers are absolutely essential in chemistry labs. Atmospheric pressure significantly changes the volume of any gas. It also alters the boiling points of liquids.
It can even speed up or slow down chemical reaction rates. Recording the exact air pressure during an experiment is crucial. It ensures other scientists can reproduce the results accurately. It lets researchers compare their findings under standard conditions.
Key facts
| Field | Physical Chemistry |
|---|---|
| Standard atmospheric pressure | 760 mmHg or 1 atm or 101.3 kPa |
| Traditional liquid | Mercury (Hg) |
| Modern alternative | Aneroid barometers use mechanical springs |
| Inventor | Evangelista Torricelli |
| Main lab use | Correcting gas volumes and boiling points |
A mercury barometer on a typical day at sea level shows a specific height. The mercury column will measure exactly 760 millimeters tall. This height equals one standard atmosphere of pressure. It is also called 760 torr. At a high altitude, there is less air pushing down. If you take the same barometer up a tall mountain, the reading changes. It might register only 630 millimeters. This lower number reflects the much thinner atmosphere and lower pressure at that height.
Frequently asked questions
Why is atmospheric pressure important in chemistry?
Atmospheric pressure affects gas volumes according to Boyle's law. It also changes boiling points and reaction rates. Standard conditions like 1 atm provide a reliable reference point for all chemical calculations.
What is the difference between a barometer and a manometer?
A barometer measures the total absolute pressure of the atmosphere. A manometer measures the pressure difference between two points. It can also measure a trapped gas pressure relative to the outside atmosphere.
Why do older barometers use mercury instead of water?
Mercury is very dense. It makes the glass tube short and manageable. A water barometer would need a tube over 30 feet tall to measure normal air pressure.