Final answer:
A state function is a property that describes a system at equilibrium based solely on its current state, not on its history. Entropy is an example of a state function. The Reaction Quotient (Q) helps to determine if a system is at equilibrium or to predict the reaction direction towards equilibrium.
Step-by-step explanation:
The property of a system that describes quantitatively the equilibrium of the system irrespective of how the system arrived at that state is known as a state function. Examples of state functions include internal energy, enthalpy, and entropy. These properties depend only on the current state of the system and are independent of the system's history or the path it took to reach that state.
In thermodynamics, the concept of a state function is important because it allows for the prediction of the system's behavior solely based on its initial and final states, without needing to know the specific processes or steps that occurred in between.
One notable state function is entropy (S), which was introduced by Clausius in 1865. Entropy measures the disorder within a system and its change is only dependent on the initial and final states of that system.
The Reaction Quotient (Q) also plays a role in understanding equilibrium. While Q itself is not a state function, it is used to determine if a system is at equilibrium (Q = K). If Q is not equal to the equilibrium constant (K), it indicates the direction in which a reaction must proceed to reach equilibrium, either forward (Q < K) or reverse (Q > K).