Joule
Definition and meaning of Joule in chemistry.
Joule is the SI unit of energy, work, or heat, equal to the energy transferred when a force of one newton acts through a distance of one meter. It can also be expressed as one watt of power applied for one second.
In more detail
The joule is named after physicist James Prescott Joule and represents a relatively small amount of energy in everyday contexts. For example, raising a 100-gram apple one meter against gravity requires approximately one joule. This unit appears throughout chemistry and physics to describe energy changes in reactions, phase transitions, and molecular processes. The joule is fundamental to understanding thermodynamics and energy conservation in chemical systems.
Key facts
| Symbol | J |
|---|---|
| Equivalent | 1 N·m = 1 kg·m²/s² = 1 W·s |
| Named after | James Prescott Joule (1818-1889) |
| Field | Physical Chemistry |
When 1 mole of ideal gas absorbs 2,500 joules of heat while expanding against atmospheric pressure, this energy distributes between increasing the internal energy of the gas and doing work against the external pressure.
Frequently asked questions
How is a joule related to calories?
One calorie (cal) equals approximately 4.184 joules, a conversion essential in food energy and thermochemistry.
What's the difference between a joule and a watt?
A joule is a unit of energy, while a watt is a unit of power (energy per unit time).