Thermodynamics Entropy question

In summary, the conversation discusses finding the entropy change of a 10-kg block of copper that is thrown into a large lake at 280K. The participants consider using the equation q=T\,dS to calculate the change in entropy for the system and surroundings. They also discuss the approach of integrating the heat capacity to find the heat transfer, and then dividing by the temperature to find the change in entropy.
  • #1
physstudent1
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Homework Statement



A 10-kg block of copper is initially 100 degrees celsius. It is thrown into a very large lake that is 280K. What is the entropy change of the piece of copper. What is the entropy change of the universe?

Homework Equations





The Attempt at a Solution


I know that the entropy change of the universe is the change of the system and the change of the surroundings. I Don't really know how to go about this problem. I know for say two copper blocks next to each other I can do ncdeltaT + ncdeltaT and b/c they have the same mass and C it is easy. however I'm assuming this won't work for a few reasons in this problem because the lake I'm pretty sure I am supposed to assume is infinite compared to the copper Can anyone help pleaseee?
 
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  • #2
I think you need to think about the energy associated with heating the copper, and about finding the resulting entropy change by integrating an equation like [itex]q=T\,dS[/itex].
 
  • #3
I worked out a solution let me see what you think(i was thinking something sort of like what you said)

I said change in internal = Q and changein internal is the integral from 373 to 280 of the C for copper which is 2.723/8.314(which is R) in my book dT (my book gives C's in Cp/R for some reason) Anyway after this integral is found I multiplied by 8.314 to get rid of the R then I said change in entropy for system is this value over 373 and for surr is the negative Q over 280 does this seem correct?
 
  • #4
Just dividing the energy by 373 K isn't going to work for the copper; some of this energy is transferred when the copper is at 373 K, some at 303 K (for example), and some at 280 K. Try integrating the dS equation as I mentioned earlier.
 
  • #5
so to get Q i do use the integral of C from 373 to 280 and then i take that and put it over T and do an integral from 373to 280 dT right?
 
  • #6
Exactly. And if you assume that the heat capacity is temperature independent, the first integral is quite simple.
 
  • #7
thanks a lot !
 

What is the definition of entropy in thermodynamics?

Entropy is a measure of the disorder or randomness of a system. In thermodynamics, it is often described as the amount of energy that is unavailable to do work.

How is entropy related to the second law of thermodynamics?

The second law of thermodynamics states that the total entropy of a closed system will always increase over time. This means that as energy is converted from one form to another, some of it will always be lost as unusable energy, increasing the overall entropy of the system.

What factors affect the entropy of a system?

The entropy of a system is affected by the number of particles present, the temperature, and the volume of the system. Increasing the number of particles, temperature, or volume will generally increase the entropy of a system.

What is the unit of measurement for entropy?

In thermodynamics, entropy is typically measured in joules per Kelvin (J/K). However, it can also be expressed in other units, such as calories per Kelvin (cal/K) or Boltzmann's constant (k).

What is the difference between reversible and irreversible processes in terms of entropy?

In a reversible process, the entropy of a system remains constant, while in an irreversible process, the entropy of the system increases. This is because reversible processes are able to return the system to its initial state, while irreversible processes result in a net increase in entropy.

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