Quantities that do vary with the size of a system are _extensive variables._ Notice that in many contexts we ignore the size of the system and use _densities_ or _[molar quantities](mole.md#Molar%20quantity)_ instead. molar quantities are generally denoted with [lower-case variables.](extensive%20variables.md#List%20of%20extensive%20variables) # List of extensive variables It may seem obvious which variables are extensive, but it's good to list them just in case, because there are a lot of them and keeping track of these things helps with problem solving. * Number of particles/subsystems, $N$ * energy, $E$ * [entropy](entropy.md), $S$ * [Gibbs Free energy,](Gibbs%20Free%20energy.md) $G$ * [heat capacity](heat%20capacity.md), $C$ #StatisticalPhysics