Problem 7 - A Complete Resource Book in Chemistry for JEE Main

Question

In thermodynamics, a process is called reversible when (a) the surroundings are always in equilibrium with the system (b) there is no boundary between system and sur roundings (c) the surroundings and system change into each other (d) the system changes into the surroundings sponta neously

Step-by-Step Solution

Answer

The correct answer is (a): the surroundings are always in equilibrium with the system.

Step 1: Understanding the Concept of Reversible Process

In thermodynamics, a reversible process is defined as one where the system and its surroundings can be returned to their original states by infinitesimal changes in some property.

Step 2: Anayzing the Conditions for Reversibility

For a process to be reversible, all changes within the system and surroundings happen in such a way that the system is always in equilibrium with the surroundings. This ensures that every change can be reversed.

Step 3: Evaluating Each Option Against the Definition

- Option (a) means the surroundings are in equilibrium with the system which aligns with the reversible process definition. - Option (b) mentions no boundary, which doesn't define reversibility. - Option (c) is not related to the equilibrium condition. - Option (d) is about spontaneous change which doesn’t fit reversibility.

Step 4: Selecting the Correct Option

Based on the definition of a reversible process and the analysis of the options, the correct choice which matches the conditions for reversibility is option (a).

Key Concepts

Understanding Thermodynamics

Thermodynamics is a branch of physics that deals with the relationships between heat, work, temperature, and energy. It explores how energy is transferred in a system and the physical laws governing these processes.
In thermodynamics, we often refer to principles like the conservation of energy, where energy cannot be created or destroyed but can change forms. Some key aspects of thermodynamics include:

• The first law of thermodynamics, which is essentially the law of energy conservation.
• The second law, which introduces the concept of entropy, indicating the direction of thermodynamic processes.
• The third law, which allows us to measure the absolute entropy of a system as it approaches absolute zero temperature.

Understanding these laws helps us to analyze systems, predict changes, and comprehend the principles of reversible processes.

The Nature of Equilibrium in Thermodynamics

Equilibrium is a crucial concept in thermodynamics which refers to a state where there are no net macroscopic flows of matter or energy.
This means the state variables like pressure, temperature, or chemical potentials are uniform throughout the system. When a system is in equilibrium:

• There is a balance of forces, meaning no unbalanced forces acting within the system.
• The process can move in either direction, depending on infinitesimal changes.

For a reversible process, the system must remain in equilibrium with its surroundings at all times.
This means if we slightly change any variable, the system and surroundings can return to the original state, without any net change in entropy. Such delicate balancing acts define the reversible nature of a process.

Understanding System and Surroundings

In thermodynamics, it's crucial to define what we are studying. This is done through the terms 'system' and 'surroundings'.
The system is the part of the universe we are focusing on, and the surroundings are everything else. Here are a few points about systems and surroundings:

• The boundary between the system and surroundings can be real or imaginary and determines what is considered part of the system.
• Changes to the system will often affect the surroundings and vice versa.
• When studying thermodynamic processes, understanding the interaction between these two is critical.

Reversible processes depend greatly on the precise nature of interactions between the system and its surroundings.
The system must be able to interchange energy with the surroundings in a perfectly controlled manner, so that every step of the process can be reversed without losses.