Question

'Icebergs' are less ordered than ice. Compare the entropy per molecule of inserting a nonpolar solute into water with the entropy of freezing water.

Short answer

Freezing water decreases entropy more than inserting a nonpolar solute into water.

Step-by-step solution

- Explain Entropy

Entropy is a measure of the disorder or randomness in a system. A higher entropy indicates a more disordered system, while a lower entropy indicates a more ordered system.

- Entropy of Inserting a Nonpolar Solute into Water

When a nonpolar solute is inserted into water, the water molecules arrange themselves in a more ordered structure around the solute. This is because nonpolar substances do not interact favorably with water molecules, and water molecules form a 'cage' like structure called clathrate. Thus, the entropy decreases since the arrangement becomes more ordered.

- Entropy of Freezing Water

When water freezes, it forms ice, which is a highly ordered structure compared to liquid water. Thus, the entropy decreases significantly because the liquid water molecules which were in a random arrangement now form an organized crystal lattice.

- Compare the Two Processes

In both cases, entropy decreases, but the extent differs. Freezing water results in a much larger decrease in entropy compared to inserting a nonpolar solute into water. This is because forming ice involves a transition from a highly disordered liquid to a highly ordered solid state.

Key concepts

Understanding Entropy

Entropy is a fundamental concept in thermodynamics. It measures the randomness or disorder in a system. The more disordered a system is, the higher its entropy. For example, a gas, with its freely moving particles, has higher entropy than a solid, where particles are fixed in a structured pattern. Scientists often use entropy to predict how processes will evolve, since systems tend to move toward a state of higher entropy. Thus, understanding entropy is crucial for studying different states of matter and their transformations.

Nonpolar Solutes and Water

When a nonpolar solute, like oil, is added to water, the water molecules organize themselves around the solute. Nonpolar substances do not mix well with water because they do not form hydrogen bonds with water molecules.
This organization forms a 'cage-like' structure known as a clathrate. This process of forming clathrates increases order in the system, which leads to a decrease in entropy. In essence, adding a nonpolar solute to water makes the water molecules more ordered, thus reducing entropy.

Clathrate Structure

The clathrate structure is a unique way in which water molecules arrange themselves around a nonpolar solute. This happens because water molecules prefer to stick to each other rather than interact with nonpolar molecules.
So they form a cage around the solute, maximizing their interactions while minimizing disruption. This structure is more ordered compared to the natural disorder of liquid water molecules, resulting in a lower entropy. Clathrate hydrates are significant in nature and have applications in gas storage and separation.

Comparing Entropy in Freezing Water

When water freezes, it undergoes a phase transition from liquid to solid. In liquid water, molecules move freely and are in a disordered state, corresponding to high entropy.
Upon freezing, these molecules form a fixed and highly ordered crystal lattice known as ice. This transformation results in a significant drop in entropy since the system goes from a disorderly state to an orderly one. Compared to the insertion of a nonpolar solute into water, freezing water results in a much larger decrease in entropy.

• This is because forming ice entails a complete reorganization of molecules into a solid state.
• Inserting a nonpolar solute only partially orders the surrounding water molecules.