Question

Explain why dissolving a solid almost always leads to an increase in disorder.

Short answer

Dissolving increases disorder because it disrupts the solid's structure, allowing for more random particle arrangements.

Step-by-step solution

Understanding Disorder

Before we start, let's understand what we mean by 'disorder.' In thermodynamics, disorder is related to the concept of entropy. Entropy measures the number of ways the particles of a system can be arranged and the energy distributed. A higher entropy means more disorder.

Initial State of a Solid

A solid consists of particles organized in a specific and structured manner, meaning low entropy and low disorder. The particles are held together in fixed positions by strong forces.

Process of Dissolving

When a solid dissolves, its particles are dispersed into a solvent (like water). This breaks the organized structure of the solid as the solute particles start to mix randomly among the solvent particles.

Resulting Increase in Entropy

This process increases the number of possible arrangements for the particles since they are now free to move about and mix across the solvent. This increase in the number of arrangements leads to an increase in entropy.

Comparing Before and After Dissolution

Before dissolution, particles are in a structured, low-entropy state. After dissolution, the disorder increases as particles are randomly spread out and move more freely.

Key concepts

Thermodynamics

In the realm of thermodynamics, one key concept is entropy. Entropy can be thought of as a measure of randomness or disorder within a system. In physical processes, there is a natural tendency for energy to spread and become less ordered. This is because systems move from a state of lower entropy to higher entropy, in accordance with the Second Law of Thermodynamics. This law essentially states that the entropy of the universe always increases over time. When you melt an ice cube, or dissolve table salt in water, these processes illustrate a transition from a more ordered state to a less ordered one, increasing entropy in the process.

Dissolution Process

The dissolution process is when a solid becomes incorporated into a liquid, forming a solution. It is a common process that significantly impacts the entropy:

• Initially, the solid has an orderly arrangement of particles held in place by strong forces.
• Once introduced to a solvent, these forces are broken, allowing for a more random dispersal of particles.

This dispersal effectively increases the entropy of the system, since the particles are no longer restricted to a fixed, ordered structure. This randomness is a hallmark of the increase in disorder, illustrating why solutes can boost the disorder when dissolved into solvents.

Solid State

The solid state of matter is characterized by particles that are tightly packed in a structured and cohesive order.

• This structure is maintained by strong forces that firmly hold the particles together.
• The fixed positions of particles result in low entropy because the arrangement has a limited number of configurations.

Being in such a state means there's minimal freedom for particle movement. However, when a solid transitions to a liquid or dissolves, the freedom of movement increases, leading to greater entropy as particles can occupy a larger variety of positions.

Particle Arrangement

The arrangement of particles is essential in determining the level of disorder in a system. In solids, particles are organized in regular patterns or lattice structures:

• This organization results in low entropy due to few ways to rearrange particles.
• Randomizing particle positions increases entropy since there are more available arrangements.

When a solid dissolves in a solvent, the ordered particle arrangement is disrupted. Consequently, the particles can move freely in the solvent, drastically altering their arrangement and increasing entropy. This leads to the conclusion that more arrangements result in higher levels of disorder in the system.