Work
Definition and meaning of Work in chemistry.
Work is energy transferred to or from a system by a force acting over a distance. In chemistry, work most commonly refers to pressure-volume work occurring when a gas expands or is compressed.
In more detail
Work is one of two primary mechanisms of energy transfer in thermodynamic processes, the other being heat. It is fundamental to the first law of thermodynamics, which states that the change in internal energy equals heat plus work: ΔU = q + w. Using the standard IUPAC sign convention, work done by a system (such as a gas expanding against external pressure) is negative, while work done on a system (such as compression) is positive, following the relationship w = -P_ext × ΔV for constant pressure processes. This sign convention reflects whether energy leaves the system (negative) or enters it (positive).
Key facts
| Symbol | w (or W) |
|---|---|
| SI Unit | joule (J) or kilojoule (kJ) |
| IUPAC convention | w = -P_ext × ΔV (expansion gives negative work) |
| Field | Physical Chemistry |
When a gas confined in a cylinder expands and pushes a piston outward against atmospheric pressure, the expanding gas does work on its surroundings, transferring energy outward (w is negative).
Frequently asked questions
What is the difference between work and heat?
Both are forms of energy transfer across system boundaries. Heat flows due to temperature differences; work results from organized mechanical forces or pressure changes.
Why is work negative when a gas expands?
In IUPAC convention, the sign indicates the direction of energy transfer. When a system expands and does work on its surroundings, energy leaves the system, so work is assigned a negative value.