Physics Review: Thermodynamics #52 Entropy

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We will find the change in entropy, delta(S)=?, when we add 1 kg of ice at 0 degrees Celsius to a lake at 10 degrees Celsius. Assuming the lake is large enough such that the 1 kg of ice will not change the temperature of the lake.
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Title search on other plateforms: Physics Review: Thermodynamics #53 Entropy and Probability

[@jakubkusmierczak695]

Mr. Professor entropy increases with the increase of temperature. When we put ice to the lake (what is negligible) we did not increase the temperature but we even decreased it. How the total amount of entropy increases?

[@HighTech636]

First the ice melts, so its entropy is increasing. And the lake loses heat, so its entropy decreases. That much is clear. What you must consider is that the ice melts at a lower temperature (@ 0 degC) than the temperature that the lake water loses heat (@ 10 degC). Hypothetically, even if you consider that the lake is actually decreasing in temperature(although we’re told this is negligible), the average temperature of this process is still larger than the temperature of the ice melting. Thus, there is still a larger increase in entropy of the ice than the subsequent decrease in the water of the lake.

[@MichelvanBiezen]

Entropy increases whenever energy is TRANSFERRED from one object to another.

[@jakubkusmierczak695]

@@HighTech636 thank You. So if we put ice in to the chilled water (0 oC) there will be no change in entropy? (what is the entropy of super cooled water? - liquid state below 0 oC is it greater than ice?)

[@jakubkusmierczak695]

@@MichelvanBiezen thank You.

[@HighTech636]

@@jakubkusmierczak695 For your first question: If you placed a single block of ice into water that has a temperature of exactly 0 degC, over time some of the water will become ice and some of the ice will become water. These phase changes actually increase the entropy of the whole system. In fact, you’re touching on a very important point. In a completely isolated system, it would be wrong to assume that entropy isn’t increasing. Recall that entropy is also a measure of the disorder of a system. A single block of ice, (which is H20 in a crystal lattice) is more ordered than several teeny tiny bits of ice distributed throughout the water continuously undergoing phase transitions, which is what this system would tend toward as it moves towards equilibrium. This second question is another great question getting to the heart of the fundamentals of thermodynamics. First and foremost let’s just acknowledge the fact that the entropy of a liquid is higher than the entropy of its solid. This is true even for super cooled water. Now, what I think you’re getting at concerns what would happen if one put a chunk of ice (@ 0 degC) into supercooled water which is at some temperature below 0 degC. Wouldn’t the super cooled water freeze and subsequently decrease in entropy? And wouldn’t this process be occurring at a lower temperature than the process of the ice melting? The answer has to do with the latent heat of fusion. When the super cooled water freezes, it actually releases energy, the heat of fusion. And this heat actually melts the ice. This results in the melted ice (i.e. water) now having a higher average temperature than initial temperature of the water (which was super cooled). So, yes, the negative change in entropy for the freezing of supercooled water is larger in magnitude than the melting of the ice, however, energy gets released in the form of latent heat as the super cooled water freezes, which melts the ice and ultimately increases the overall entropy of the system

[@Znxjsjnsdn]

Professor how do you know the sidereal year accounts for precession and tropical doesn’t?

[@MushiSaad1]

Hello sir. This is kind of off topic but I just have a question, why do you know so much about different topics? Do you simply love learning and sharing knowledge with others or is there some educational background that required it? Thanks in advance

[@MichelvanBiezen]

A lifetime of learning as well as working as an engineer and teaching multiple subjects in college.