Question

Which of the following processes are spontaneous and which are nonspontaneous: (a) dissolving table salt \((\mathrm{NaCl})\) in hot soup, (b) climbing \(\mathrm{Mt}\). Everest, (c) spreading fragrance in a room by removing the cap from a perfume bottle, (d) separating helium and neon from a mixture of the gases?

Short answer

(a) and (c) are spontaneous, (b) and (d) are nonspontaneous.

Step-by-step solution

Understand Spontaneity

Spontaneous processes occur naturally without any outside intervention, leading to an increase in the disorder or entropy of the system. Nonspontaneous processes require external energy to proceed.

Evaluate Each Process

**(a) Dissolving Salt in Soup:** When table salt is placed in hot soup, it dissolves, forming ions that disperse in the liquid. This process increases the entropy or randomness of the ions in the soup and is generally spontaneous. **(b) Climbing Mt. Everest:** Climbing requires external energy, typically from a person’s exertion, and involves working against gravity, making it nonspontaneous without external effort. **(c) Perfume Fragrance Spreading:** When you remove a cap from a perfume bottle, the fragrance molecules naturally spread out from the high concentration inside the bottle to the lower concentration in the room, leading to increased entropy and a spontaneous process. **(d) Separating Helium and Neon Gases:** This separation requires energy to distinguish and move each type of gas into separate areas, making it a nonspontaneous process.

Conclude on Nature of Each Process

Summarizing the analysis: (a) is spontaneous, (b) is nonspontaneous, (c) is spontaneous, and (d) is nonspontaneous.

Key concepts

Entropy

Entropy is a fundamental concept in chemistry that describes the measure of disorder or randomness in a system.
When a system undergoes a change, the entropy either increases or decreases.
Generally, natural processes tend to move towards an increase in entropy, aligning with the second law of thermodynamics.

• High entropy indicates a high level of disorder.
• Low entropy means the system has more order.

For example, when salt dissolves in water, it results in a higher entropy because the orderly structure of solid salt breaks apart into free-moving ions.
By understanding entropy, we gain insights into the directionality and possibility of reactions and processes.

Spontaneous processes

Spontaneous processes are changes that occur naturally without any external influence. These processes typically lead to an increase in entropy.
The key to identifying a spontaneous process is identifying a natural progression towards disorder or energy dispersal.

• Spontaneous processes do not need external energy to proceed.
• They are often irreversible under normal conditions.

A classic example is the spreading of a fragrance, where molecules naturally diffuse throughout the available space.
As a result, the odor travels from a concentrated area to a less concentrated one, signifying a spontaneous progression.

Nonspontaneous processes

Nonspontaneous processes, unlike spontaneous ones, require external energy to proceed.
These processes often lead to a decrease in entropy or need energy input to maintain order, going against the natural inclination towards disorder.

• They are not self-sustaining and typically reversible if the external energy is removed.
• Increasing entropy is often resisted in these processes.

An example is climbing Mt. Everest, which requires significant energy input from climbers, going against gravitational forces and natural entropy increase to reach the summit.

Chemical dissolution

Chemical dissolution occurs when a solute dissolves in a solvent, creating a homogeneous solution. This process often increases the system's entropy.

• Ions or molecules of the solute disperse amongst the solvent particles.
• The process is typically spontaneous if the solute and solvent are compatible.

For instance, dissolving salt in hot soup involves breaking down its lattice structure, allowing ions—the smallest units of NaCl—to spread uniformly in the liquid.
The random distribution of ions compared to their solid state results in a greater disorder and higher entropy.

Gas separation

Gas separation involves dividing components of a gas mixture into individual gases.
This process aims to increase order, typically making it nonspontaneous due to the energy required for separation.

• Equipment and energy are necessary to perform these separations.
• Often used in industries, such as helium and neon separation.

The innate mixing tendency of gases due to their high entropy leads them to stay mixed rather than separate.
Thus, external energy is required to separate them, moving against the natural entropy increase that occurs in unassisted processes.