Physics of paper absorbing Water -- Doesn't this decrease Entropy?

In summary, the conversation discusses the hydrophilic quality of cellulose and its polarity due to the hydroxyl groups. The combination of adhesive and cohesive forces allows water to overcome gravity when a piece of paper is placed in it. The group also questions why water prefers to form hydrogen bonds with cellulose and how it brings the system into a lower energy state. It is also noted that this process may decrease entropy, but only locally. The conversation then delves into the connection between hydrogen bonding and the 2nd law of thermodynamics, discussing how closed systems evolve into lower potential energy states which can manifest as higher temperature and entropy.
  • #1
casparov
29
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Summary: doesn't this decrease entropy ?

Cellulose is known for its hydrophilic quality, which can be explained from the polarity of its hydroxyl groups.

We all know water can overcome the force of gravity through a piece of paper you put in the water.
Correct me if I'm wrong but this is a combination of adhesive + cohesive forces > gravity.

Why is it favorable for the water to form hydrogen bonds with the cellulose, why favorable to maximize those bonds? Is it because of higher electronegativity of the hydroxyls than the water molecules in the liquid?

How does it bring the system into a lower energy state?

Doesn't it also decrease entropy ? Or only in a very local way, because water found some air pockets inside the paper, therefore increasing the degrees of freedom ?

and more general how does hydrogen bonding rhyme with 2nd law of thermodynamics ?
 
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  • #2
casparov said:
How does it bring the system into a lower energy state?

Doesn't it also decrease entropy ?
Energy is conserved, hence closed systems do not evolve into lower energy states. Instead, they evolve into lower potential energy states. Why? Because lower potential energy means higher kinetic energy (because total energy is conserved), and kinetic energy can take the form of thermal motion, which means higher temperature and hence higher entropy.
 
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Likes Lord Jestocost and vanhees71

1. How does paper absorb water?

Paper is made up of cellulose fibers, which have a high affinity for water molecules. These fibers create tiny spaces in the paper that can hold water, allowing it to be absorbed.

2. Why does paper absorb water?

Paper absorbs water due to a process called capillary action. This is when the water molecules are attracted to the cellulose fibers in the paper, and are able to move through the tiny spaces between the fibers.

3. Does paper absorbing water decrease entropy?

Yes, the process of paper absorbing water does decrease entropy. Entropy is a measure of the disorder or randomness of a system, and when water is absorbed by the paper, the water molecules become more organized in the paper's fibers, decreasing the overall entropy of the system.

4. How does the decrease in entropy affect the paper?

The decrease in entropy caused by paper absorbing water can lead to changes in the physical properties of the paper. For example, the paper may become softer or more pliable, and may also change in size or shape due to the movement of water molecules within the paper.

5. Can the entropy of paper absorbing water be reversed?

Yes, the decrease in entropy caused by paper absorbing water can be reversed by drying the paper. When the water evaporates from the paper, the water molecules become more disordered and the entropy of the system increases again.

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