Exploring Negative Entropy: Understanding the Standard Molar Entropy of OH-

In summary, the conversation discusses the standard molar entropy of H+, H2O, and OH-. The standard molar entropy of H+ and H2O is positive, but OH- has a negative standard molar entropy. The person asking the question is trying to understand why OH- has a negative entropy and the response explains that this is likely due to the addition of the molecule to water increasing order. They also mention that the reference point for measuring entropy may be higher in this case.
  • #1
Trowa
6
0
Hi there!

The Standard molar entropy of H+ and H2O are positive.
But OH- has a negative standard molar entropy.
Can somebody explain why the standard molar entropy of OH- is negative?

I just can't imagine how entropy could be negative.

Thanx in advance!
 
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  • #2
What reference are you looking at?
 
  • #3
Mapes said:
What reference are you looking at?

Physical chemistry (Atkins) - 8th edition
And this question appeared on my exam.

Do you know more about negative entropy?
 
  • #4
It looks like Atkins is talking about the partial molar entropy of the molecule in solution; the addition of the molecule to water increases order.
 
  • #5
That makes sense; pure OH- could than still be positive but that is hard to isolate. Maybe the entropy is lower in water because the anions can be closer together than without solution (strong repulsion) (basically: the reference point must be higher in entropy).

Thanx!
 

1. What is entropy and why is it important?

Entropy is a measure of the randomness or disorder in a system. It is important because it helps us understand and predict the behavior of physical and chemical systems, such as the direction of chemical reactions or the flow of heat.

2. Can entropy be negative?

Yes, entropy can be negative. This occurs when a system becomes more ordered or organized, leading to a decrease in randomness. However, this is not a common occurrence and typically only happens in very specific conditions.

3. How can entropy be negative if it is a measure of disorder?

While entropy is commonly associated with disorder, it is more accurately a measure of the number of microstates available to a system. Therefore, a decrease in entropy can occur when a system goes from a state with many possible microstates to a state with fewer possible microstates, even if that state appears more orderly.

4. What are some examples of negative entropy?

One example of negative entropy is the formation of a crystal. When a liquid solidifies into a crystal, the molecules become more ordered and the entropy decreases. Another example is the growth of a living organism, as it becomes more organized and complex over time.

5. Is negative entropy always favorable?

No, negative entropy is not always favorable. While it may seem counterintuitive, sometimes an increase in disorder or randomness is necessary for a system to reach a more stable or energetically favorable state. This is seen in processes like diffusion, where an increase in entropy is necessary for particles to move from a more concentrated to a less concentrated area.

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