I learnt that Gibbs free energy is the maximum amount of non-expansion work. But the phrase non expansion work confuses me. Work is defined as pressure times change in volume. If there is no expansion, how can work be done?
Pressure-Volume work is a type of mechanical work .
There are also non-mechanical forms of work where in pressure and volume terms are not involved .
The most famous example is electrical work . The work done to move electrical charges ( like motion of electrons in a conductor) comes under this category .