Change in entropy of the universe due to some block being lifted

In summary, a 1kg block of steel at a temperature of 60 degrees is placed at the bottom of a 10m deep lake at a temperature of 10 degrees. After reaching thermal equilibrium, the change in entropy for the block is 68.3, the change in entropy for the lake is zero due to the insignificant temperature change, and the change in entropy for the universe is positive as energy is being transferred. After slowly lifting the block to the surface, the change in entropy for the universe would most likely be zero.
  • #1
blueyellow
a 1kg block of steel at temperature 60 degrees is placed at the bottom of 10m deep lake at temprature 10 degrees. the specific heat capacity of steel is 420J/Kkg and is approximately temperature independent.calculate the entropy change of the block, the lake and the universe,after thermal equilibrium has been reached

i did the change in entropy=420 ln ((60+273.16)/(10+273.16))=68.3

so the change in entropy of the block is 68.3, the change in entropy of the lake is zero because the change in temperature of the lake is insignificant and the change in entropy of the universe is the same as the change in entropy of the block.right?

AND

after thermal equilibrium, a crane is used to life the block extremely clowly from the bottom of the lake to the surface, what is the entropy change of the universe?
how am i supposed to know? do i have to take into account the temperature of the surface of the lake/air? we arent told the temperature of the air
 
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  • #2
i think you are right in the first part.

in 2nd part, i think change in entropy should be zero, as thermal equilibrium is reached.
 
  • #3
blueyellow said:
so the change in entropy of the block is 68.3, the change in entropy of the lake is zero because the change in temperature of the lake is insignificant

Whoa. (1) How does the block gain entropy if it is cooling down? (2) The change in entropy of the lake isn't negligible, even if the temperature change is.

The block is dumping energy into the lake; we should expect the block's entropy to decrease and the lake's to increase. And we should expect the entropy change of the universe to be positive for any spontaneous process.
 

What is entropy?

Entropy is a measure of the disorder or randomness in a system. It is often described as the amount of unavailable energy in a system.

What causes a change in entropy?

A change in entropy can be caused by any process that increases or decreases the disorder or randomness in a system. This can include physical processes, chemical reactions, and even changes in temperature or pressure.

How is entropy related to the universe?

The concept of entropy is closely tied to the laws of thermodynamics, which govern the behavior of energy in the universe. The second law of thermodynamics states that the total entropy of a closed system (like the universe) will always increase over time.

How does lifting a block affect the entropy of the universe?

Lifting a block may seem like a small and insignificant action, but it actually has an impact on the entropy of the universe. This is because the act of lifting the block requires energy, and energy is always lost in the form of heat, increasing the overall entropy of the universe.

Can the entropy of the universe ever decrease?

According to the second law of thermodynamics, the total entropy of the universe will always increase. This means that while local decreases in entropy may occur, the overall trend will always be towards an increase in entropy.

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