Question

Spontancous mixing of two gases by diffusion is (1) reversible (2) irreversible (3) exothermic (4) endothermic

Short answer

irreversible

Step-by-step solution

Understand the Concept of Diffusion

Diffusion is the process by which molecules spread from areas of high concentration to areas of low concentration until they are evenly distributed.

Analyze Reversibility

A reversible process is one where the system and surroundings can be returned to their original states. Spontaneous mixing of gases by diffusion is not easily reversed because once mixed, separating the gases back into their original concentrations requires additional work.

Evaluate Irreversibility

An irreversible process is one that cannot easily be undone. Diffusion leads to increased entropy, making it an irreversible process since it’s difficult to reverse the mixing without external intervention.

Assess Thermodynamic Nature

Exothermic and endothermic refer to whether a process releases or absorbs heat. Diffusion is typically driven by concentration gradients and not by heat exchange.

Conclude Based on Analysis

Based on the properties analyzed, diffusion of two gases is best classified as irreversible.

Key concepts

Reversible Process

In thermodynamics, a reversible process is one where the system and its surroundings can return to their initial states without any net change to the universe. These processes are idealized concepts and do not occur naturally since they require infinitely slow changes that allow the system to remain in equilibrium at all times. For instance, if you slowly compressed a gas in a piston such that the temperature and pressure at every point were well-defined and uniform throughout, this would be considered nearly reversible. However, in real life, every process has some degree of irreversibility due to factors like friction, turbulence, and thermal gradients.

Irreversible Process

An irreversible process, in contrast, is one that cannot be returned to the initial state without leaving changes in the system or surroundings. When gases mix through diffusion, they spontaneously move from high concentration areas to low concentration areas until evenly distributed. This mixing increases the disorder or entropy of the system, making it an irreversible process. Attempting to separate these mixed gases back into their initial states requires external work and energy input, often making it impractical. A common feature of irreversible processes is the dissipation of energy in forms like heat, sound, or deformation, which cannot be easily recovered.

Entropy Increase

Entropy is a fundamental concept in thermodynamics representing the degree of disorder or randomness in a system. For a process to be spontaneous, it must increase the overall entropy of the universe. In the case of gas diffusion, when two gases mix, the entropy of the system increases because the molecules from each gas spread out and occupy the combined volume, leading to a more disordered state. This increase in entropy is a hallmark of spontaneous and irreversible processes. As the gases mix and their molecules become more randomly distributed, the system's entropy rises, indicating that reversing this process would require additional energy and work, which further signifies its irreversibility.