Question

In which of the following processes does the entropy increase? In each case, explain why it does or does not increase. (a) A bottle of ammonia is opened. The odor of ammonia is soon apparent throughout the room. (b) Sodium chloride dissolves in water (c) A protein is completely hydrolyzed to the component amino acids.

Short answer

Entropy increases in all three processes: dispersal of ammonia gas, dissolution of sodium chloride, and hydrolysis of protein.

Step-by-step solution

- Analyze the ammonia example

When a bottle of ammonia is opened, ammonia molecules, initially concentrated in the bottle, disperse throughout the room. This increased dispersal of molecules from a concentrated region to a larger volume indicates an increase in disorder. Based on the second law of thermodynamics, entropy, which is a measure of disorder, increases in this process.

- Analyze the dissolution of sodium chloride in water

When sodium chloride (NaCl) dissolves in water, the solid crystal structure of NaCl breaks down into ions (Na⁺ and Cl⁻) that are dispersed throughout the solution. This spread of ions into a solvent increases the randomness or disorder of the system. Therefore, the entropy of the system increases.

- Analyze the protein hydrolysis

In the hydrolysis of a protein, the long, complex chain of amino acids is broken down into its individual amino acids or smaller peptide fragments. Breaking down a structured, ordered protein into smaller units increases the randomness and disorder within the system. Thus, the entropy increases in this process as well.

Key concepts

Ammonia diffusion

When a bottle of ammonia is opened, the ammonia molecules begin to spread out from an area of high concentration (inside the bottle) to an area of lower concentration (the surrounding room).
This process is an example of diffusion and is a natural result of molecules moving to occupy available space evenly.
In terms of thermodynamics, the movement of molecules from a well-defined, orderly region to a more random, dispersed state is an increase in entropy.
The law of entropy, also known as the second law of thermodynamics, states that systems tend to move towards greater disorder.
When ammonia disperses throughout the room, the randomness and unpredictability of the positions of the molecules increases substantially.
This change signifies an increase in entropy, as the system has transitioned from a state of higher order to one of higher disorder and randomness.

Sodium chloride dissolution

When sodium chloride (table salt) dissolves in water, a crystal lattice of NaCl breaks down into its ions, Na⁺ and Cl⁻.
This breaking down process results in the ions dispersing freely within the water, vastly increasing their disorder.
Before dissolution, the ions are fixed in a regular, repeating pattern within a solid crystal lattice.
Once dissolved, these ions are free to move around individually within the solution.
This freedom contributes to a higher state of disorder or randomness for the system.
According to the second law of thermodynamics, this increased randomness corresponds to an increase in entropy.
In other words, when a rigid and orderly structure like a crystal dissolves into a solution, the system's overall entropy always increases.

Protein hydrolysis

Protein hydrolysis involves breaking long, complex protein chains into smaller peptide fragments or individual amino acids.
Proteins are structured and ordered molecules with amino acids linked in specific sequences.
When hydrolyzed, these structured molecules break down into smaller, less organized pieces.
The increase in the number of individual molecules and the decrease in order leads to greater randomness in the system.
This heightened randomness indicates an increase in entropy.
As per the second law of thermodynamics, natural processes tend to increase entropy.
By breaking down the ordered structure of proteins into their component parts, the process of protein hydrolysis demonstrates a clear increase in the disorder and randomness of the system.