Problem 21 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

Which one of the following statements is false? [2001S] (a) Work is a state function. (b) Temperature is a state function. (c) Change in the state is completely defined when the initial and final states are specified. (d) Work appears at the boundary of the system.

Step-by-Step Solution

Answer

Statement (a) is false because work is not a state function.

Step 1: Understanding State Function

A state function is a property of a system that depends only on the initial and final states and not on the path taken. Temperature is a classic example, as it is independent of the process path.

Step 2: Evaluating Each Statement

Let's evaluate each statement: - (a) Work is a state function: This is false because work depends on the path taken. - (b) Temperature is a state function: This is true as temperature only depends on the state of the system. - (c) Change in the state is completely defined when the initial and final states are specified: This is true for state functions. - (d) Work appears at the boundary of the system: This is true as work is one of the forms of energy transfer across the boundary.

Step 3: Identifying the False Statement

From the evaluations: - Statement (a) is false because work is not a state function, it is a path function. Other statements (b), (c), and (d) are true. Thus, the false statement is statement (a).

Key Concepts

State Function

In the realm of thermodynamics, a state function is crucial because it informs us about the property of a system based solely on its current state, irrespective of the journey it took to get there. This means that if you know the initial and final states of a system, you can determine the change in the state function, without concerning yourself with the process path. Examples of state functions include:

• Temperature
• Pressure
• Volume
• Internal energy

No matter how the system changes from one state to another, whether rapidly or slowly, the change in a state function remains constant. This is because state functions are independent of the process or path. So, when we only care about where a system starts and ends, state functions become particularly useful. They provide simplified calculations in thermodynamic equations by allowing us to focus on the initial and final states alone.

Path Function

Unlike state functions, path functions are properties that depend on the specific transitions or paths between states. In simpler terms, they are influenced by HOW the system goes from one state to another. Work and heat are classic examples of path functions in thermodynamics. To further break this down:

• Work: It can vary significantly based on the method, route, or pathway taken to implement a process.
• Heat: Similarly, the amount of heat transferred depends on the exact process undergone.

The dependency on paths means that integrating path functions over different paths yields different results, as opposed to state functions which only care about the end states. Thus, work done during a thermodynamic process cannot be determined solely by knowing the initial and final states, but instead requires detailed path data.

Work in Thermodynamics

Work, in thermodynamics, refers to the energy transfer that occurs when a force is applied over a distance or against a pressure. It is the form of energy that crosses the boundary of a system and can alter the system's state. Here are some important points about work in thermodynamics:

• Work is a path function, meaning it depends on the specific sequence of events leading between two states.
• Work appears and disappears across the boundary, often visible as changes in the surroundings, like stirring or compressing gases.
• Since it relies on the process, calculations of work can vary depending on compressing methods or expansion for example.

The unit of work is the joule (J), and its calculation often involves the integration of pressure-volume curves or force-distance scenarios. Understanding work as a path function, versus the simpler calculations of a state function, underscores why thermodynamics often focuses heavily on detailed path-dependent evaluations.