Question

A thermodynamic state function is (1) onc which obeys all the laws of thermodynamics (2) a quantity which is used to measure thermal changes (3) a quantity whose valuc is independent of the path (4) a quantity which is used to cxpress pressure volume work

Short answer

(3) a quantity whose value is independent of the path

Step-by-step solution

Understanding the Question

Determine which of the given options correctly defines a thermodynamic state function.

Assessing Option (1)

Option (1) suggests a state function obeys all laws of thermodynamics. However, this is not a defining characteristic of a state function itself.

Assessing Option (2)

Option (2) indicates it measures thermal changes. This is more characteristic of thermodynamic quantities like heat and temperature, not state functions specifically.

Assessing Option (3)

Option (3) states that a state function's value is independent of the path taken to reach that state. This accurately describes a state function.

Assessing Option (4)

Option (4) refers to expressing pressure-volume work, but this is specific to work done by/on a gas and does not define a state function.

Conclusion

After evaluating all options, it is clear that Option (3) correctly defines a thermodynamic state function.

Key concepts

Thermodynamics

Thermodynamics is a branch of physics that deals with heat, work, temperature, and the relationship between them. It describes how energy is transferred in forms of heat and work within physical systems and studies how these processes adhere to the laws of physics.

There are four primary laws of thermodynamics:

• **Zeroth Law:** If two systems are in thermal equilibrium with a third system, they are in thermal equilibrium with each other. This forms the basis for the definition of temperature.
• **First Law:** Energy cannot be created or destroyed, only transferred or changed in form. This is also known as the law of energy conservation.
• **Second Law:** The total entropy of an isolated system can never decrease over time. In other words, energy spontaneously spreads from regions of higher concentration to regions of lower concentration.
• **Third Law:** As temperature approaches absolute zero, the entropy of a system approaches a constant minimum.

Understanding these fundamentals can help students better grasp more detailed topics like state functions and path-independent variables.

State Function

In thermodynamics, a state function is a property of a system that only depends on the current state of the system, not on the path taken to reach that state.
This means that no matter how the system arrived at its current position, the value of its state function will be the same.
Examples of state functions include:

• **Temperature (T):** It measures how hot or cold a system is.
• **Pressure (P):** It measures the force exerted per unit area within the system.
• **Volume (V):** It measures the amount of space that the system occupies.
• **Internal energy (U):** It is the total energy contained within the system.

These properties are vital because they help in describing the equilibrium state of a system without needing to account for the mechanics of the changes that brought the system to that state.
When using state functions, calculations become simpler and more manageable since path-dependent details are neglected.

Path-Independent Variables

Path-independent variables, as the name suggests, are properties of a system whose values do not depend on the process or path taken to achieve that state.

These variables are equivalent to state functions.
Path-dependent variables, such as work and heat, depend on the specific transition path the system undergoes. In contrast, path-independent variables are solely dependent on the initial and final states of the system.
Examples include:

• **Enthalpy (H):** A measure of the total heat content in the system.
• **Entropy (S):** A measure of the disorder or randomness in a system.
• **Gibbs free energy (G):** Useful for determining the feasibility of processes at constant temperature and pressure.

By understanding the nature of these variables, students can better analyze thermodynamic processes without getting bogged down by the specifics of the pathways involved.