Question

Tell whether the entropy changes for the following processes are likely to be positive or negative: (a) The fizzing of a newly opened can of soda (b) The growth of a plant from seed

Short answer

(a) Positive, (b) Negative.

Step-by-step solution

Understanding Entropy

Entropy is a measure of disorder or randomness within a system. An increase in disorder generally results in a positive change in entropy, whereas a decrease in disorder leads to a negative change in entropy.

Analyzing Process (a)

Consider the fizzing of a newly opened can of soda. When the can is opened, carbon dioxide gas that was dissolved in the liquid is released into the atmosphere, increasing disorder as the gas molecules spread out and move freely compared to being confined in the liquid. Therefore, the entropy change is likely to be positive.

Analyzing Process (b)

Consider the growth of a plant from seed. This process involves the organization of cells and structures as the plant grows, resulting in a higher degree of order within the system of the plant itself. However, in the broader context of the environment, the overall entropy might still increase. Notably, for this exercise, we focus on the system level, where entropy change is generally considered negative.

Key concepts

Entropy Change

Entropy change is a crucial concept in understanding the behavior and progress of various systems. Imagine entropy as a measure of disorder or randomness within a system. When the disorder in a system increases, we say there is a positive change in entropy. On the other hand, when we see a more ordered state arise, the entropy change is negative.

To grasp this concept, consider two scenarios involving different kinds of changes:

• In a positive entropy change, gas molecules spread out. An example is when you open a soda can, releasing carbon dioxide gas, causing more chaos.
• For a negative entropy change, think about organizing objects or materials, like when a plant organizes its cells to grow, creating more order.

Positive Entropy

Positive entropy occurs when disorder or randomness in a system increases. This can be seen when systems evolve from a structured state to a more disordered one.

Take the example of opening a can of soda:

• When the soda is opened, the dissolved carbon dioxide gas escapes into the atmosphere.
• This gas transition from being confined in the liquid to being dispersed freely in the air creates higher entropy.
• The molecules moving freely demonstrate increased disorder, and thus, there is a positive change in entropy.

Positive entropy changes are a natural tendency in many reactions, often highlighting the spontaneous nature of these processes.

Negative Entropy

Negative entropy, or decreasing entropy, arises when a system becomes more ordered. This involves processes where randomness or disorder decreases, and structure or organization is enhanced.

For example, consider the growth of a plant from a seed:

• As a plant grows, cells organize into complex tissues and structures.
• This process involves energy and leads to a more ordered state within the plant.
• In terms of the system of just the plant, the entropy here is negative as the plant becomes highly organized.

However, it is important to note that while the system itself may experience a negative entropy change, the overall entropy of the surroundings, including energy exchange, may tell a different story.