What is a state function?

A state function is defined as a property of a system that is determined solely by the current state of the system, irrespective of how the system arrived at that state. This means that the value of a state function depends only on the state variables at a given moment, such as temperature, pressure, and volume, rather than the specific path taken to reach that state.

For example, when considering properties like internal energy, enthalpy, and entropy, these quantities are state functions because they are defined by the current conditions of the system. Changing the way you get to that state—including various processes or paths—will not affect the value of these properties at that state. This is in contrast to path-dependent properties, which can differ based on how the system transitions from one state to another.

In this context, other options present ideas related to properties but do not accurately define a state function. For instance, properties that are dependent on the path taken to change state do not exhibit the characteristics of state functions. Similarly, while some properties can only be measured at equilibrium, this characteristic does not universally apply to state functions and is not part of the defining nature of a state function itself.