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Homework Help: Internal Energy Question

  1. Apr 27, 2007 #1
    1. The problem statement, all variables and given/known data
    Does the internal energy increase/decrease(U), quantity of heat released or supplied (Q), and work done by or on a system (W) when
    (a) water freezes to ice at constant temperature
    (b) ice melts to water at constant temperature
    (c) water evaporates at constant temperature
    (d) water boils at constant temperature?

    2. Relevant equations
    First Law of Thermodynamics
    U = Q + W
    where U is internal energy of the system, Q is the quantity supplied to the system and W is the work done on the system.
  2. jcsd
  3. Apr 27, 2007 #2

    Chi Meson

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    Science Advisor
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    Not sure what the question is. I'm guessing, you are supposed to say whether deltaU, Q, and W is positive or negative or zero in each situation?

    To answer the deltaU part, you need to remember that internal energy is a direct function of temperature.
  4. Apr 29, 2007 #3
    Sorry, the question was asking whether deltaU, Q, and W is positive or negative or zero in each situation?

    if (a) water freezes to ice at constant temperature,
    then delta W = 0 (since work done by atmospheric pressure is negligible as volume change is small), delta Q < 0 (heat energy is released when bonds are formed during freezing) and hence by equation delta U = delta Q + delta W, delta U < 0 , ie internal energy decreases. am i right?

    how about the others?
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