# Understanding Entropy Changes in Different Chemical Reactions

• bjoyful
In summary, entropy refers to the number of states a system can be in and is affected by the number of particles present. In the example of solid sodium dissolving in water and hydrocarbons being cracked, both demonstrate an increase in entropy due to the increase in the number of particles and available states in the system. This is in contrast to the example of liquid water converting to ice, which shows a decrease in entropy.
bjoyful
I am studying about entropy increasing and decreasing. I *think* I understand the example when liquid water is converted to ice, and that it demonstrates a decrease in entropy. However, I don’t get the other two – when solid sodium is dissolved in water and when hydrocarbons with 16 carbons are cracked into smaller hydrocarbons. Are they demonstrating an entropy increase or decrease? Why?

Basically entropy signifies the number of states a system can be in. This means that when there are more particles in a system that the system can attain more states. So when solid sodium reacts with water to form sodium ions, hydrogen and hydroxide ions the system gains entropy because there will be more states for it to be in. When the hydrocarbon is cracked entropy also increases because there will be more particles in the system that can all be somewhere at some velocity which implies more states are available.

Thanks for that wonderful explanation! So they both demonstrate entropy increasing...I thought that is what it was, but now I have a better grasp on it - thanks to you:)

## 1. What is entropy and how does it relate to increases and decreases?

Entropy is a measure of the disorder or randomness in a system. In thermodynamics, it is often described as the degree of molecular disorder within a system. Entropy increases when the disorder or randomness increases, and decreases when the disorder decreases.

## 2. Why does entropy tend to increase in closed systems?

In closed systems, where there is no exchange of matter or energy with the surroundings, entropy tends to increase due to the natural tendency of particles to spread out and become more disordered over time. This is known as the second law of thermodynamics.

## 3. How does the concept of entropy apply to the universe?

The concept of entropy applies to the universe as a whole, as it is a closed system. Over time, the universe tends towards a state of maximum entropy, where all energy is evenly distributed and no work can be extracted. This is known as the heat death of the universe.

## 4. Can entropy ever decrease in a system?

In isolated systems, where there is no exchange of matter or energy with the surroundings, entropy can theoretically decrease. However, this would require a highly improbable and carefully controlled scenario, as the natural tendency is for entropy to increase.

## 5. How does the concept of entropy relate to the arrow of time?

The concept of entropy is closely related to the arrow of time, as entropy tends to increase in one direction of time. This is because the increase in entropy is a measurable and observable phenomenon, while the reverse (decrease in entropy) is not. This is known as the thermodynamic arrow of time.

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