SYSTEM: OPEN

Concept Quiz

The First Law of Thermodynamics

The behavior of thermodynamic systems is governed by the conservation of energy. The internal energy ($U$) changes when heat ($q$) is added/removed, or when work ($w$) is done on/by the system. The type of boundary determines what can cross it.

$$ \Delta U = q + w $$
Open System: Exchanges Mass ($\Delta m \neq 0$) & Energy ($\Delta U \neq 0$)
Closed System: Exchanges Energy ($\Delta U \neq 0$), but Mass is constant ($\Delta m = 0$)
Isolated System: Cannot exchange Mass or Energy ($\Delta m = 0$, $\Delta U = 0$, $q = 0$, $w = 0$)