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So basically i am asking is entropy conserved?

  1. Mar 31, 2004 #1
    The other day in class we were reviewing for the AP Chem test and came across a question regarding Entropy, the question was

    If you put an ice cube in a container of hot water and sealed it completely, how would the entropy and energy values change?

    I answered that Energy and Entropy would remain constant because all the energy from the water would go to the ice and all the entropy lost by the water would go to the ice.
    The correct answer was that the energy would remain constant and the entropy would increase.

    So basically i am asking is entropy conserved???
    Last edited by a moderator: Jan 7, 2014
  2. jcsd
  3. Mar 31, 2004 #2

    Doc Al

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    Staff: Mentor

    No, entropy is not conserved. In general, for a closed system, such as the sealed container in your example, the total entropy cannot decrease but can only increase (or stay the same). In this particular example, the thermal energy redistributes to maximize entropy. Once thermal equilibrium is reached, the entropy will remain constant.
  4. Mar 31, 2004 #3

    Chi Meson

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    To continue:

    there is no "conservation of entropy" law. In fact, there is the second law of thermodynamics which says, specifically, that entropy always increases.

    WE can't measure total entropy, but we can measure the change in entropy: In your hot water/ice situation, the ice is at 273 K and the water is at, let's say 350 K. THe change in entropy of the ice is found by dividing the heat that goes into it, over the temperature of the ice (+Q/T_cold). This produces an increase in entropy of the ice.

    Of couse the heat that goes into the ice comes out of the water. Let's say that there is enough water at 350 K so that the temperature stays constant. The reduction of entropy in the water = the heat that leaves the water over the temperature of the water (-Q/T_hot). Q is the same for the water and the ice, but since T_hot is greater than T_cold, the increase in entropy of the water is more than the decrease in entropy of the water.
  5. Mar 31, 2004 #4
    Thanks it makes sense now. My teacher told me to just think of entropy changes from gas to liquid to solid for the chemistry test
  6. Mar 31, 2004 #5
    Just stick with the states of matter dealing with entropy at the AP chem level.
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