State functions are properties of a system that depend only on the current state of the system, not on the path taken to reach that state. Think of it like hiking to the top of a mountain. The change in your elevation is the same whether you take a winding trail or a direct route straight up. Common examples of state functions in chemistry include internal energy ($U$), enthalpy ($H$), entropy ($S$), and Gibbs free energy ($G$). Changes in these properties (e.g., $\Delta U$, $\Delta H$) are what we often calculate because they tell us about the difference between the initial and final states.
Understanding state functions simplifies many thermodynamic calculations. Because they are path independent, we can use Hess's Law, for example, to calculate enthalpy changes using any convenient series of reactions, regardless of the actual reaction pathway.
Match the following terms with their definitions:
| Term | Definition |
|---|---|
| 1. Enthalpy | A. The measure of disorder in a system. |
| 2. Entropy | B. A function that combines enthalpy and entropy to determine spontaneity. |
| 3. Gibbs Free Energy | C. The total energy of a system plus the product of its pressure and volume. |
| 4. Internal Energy | D. A function whose value depends only on the current state of the system, not how it got there. |
| 5. State Function | E. The total energy contained within a thermodynamic system. |
Match the term to the appropriate definition.
Complete the following paragraph using the words provided: path, state, independent, Hess's Law, functions.
State __________ are properties that are __________ of the __________ taken to reach a particular __________ . This allows us to use __________ to calculate enthalpy changes efficiently.
Explain why knowing that enthalpy is a state function is useful in thermochemistry. Provide a real-world example to support your answer.
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