Work Definition in Chemistry

The work required to carry a ball up a hill is the energy needed to act against the force of gravity.
The work required to carry a ball up a hill is the energy needed to act against the force of gravity. Michael Blann / Getty Images

The word "work" means different things in different contexts. In science, it is a thermodynamic concept. The SI unit for work is the joule. Physicists and chemists, in particular, view work in relation to energy:

Work Definition

Work is the energy required to move an object against a force. In fact, one definition of energy is the capacity to do work. There are many different kinds of work. Examples include:

  • Electrical work
  • Work against gravity
  • Work against a magnetic field
  • Mechanical work

Mechanical Work

Mechanical work is the type of work most commonly dealt with in physics and chemistry. It includes work moving against gravity (e.g., up an elevator) or any opposing force. Work is equal to the force times the distance the object moves:

w = F*d

where w is work, F is the opposing force, and d is the distance

This equation may also be written as:

w = m*a*d

where a is the acceleration

PV Work

Another common type of work is pressure-volume work. This is work done by frictionless pistons and ideal gases. The equation to calculate the expansion or compression of a gas is:

w = -PΔV

where w is work, P is pressure, and ΔV is the change in volume

Sign Convention for Work

Note that equations for work employ the following sign convention:

  • Work performed by the system on the surroundings has a negative sign.
  • Heat flow from the system into the surroundings has a negative sign.