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Homework Help: How to define dynamic equilibrium

  1. Mar 3, 2005 #1
    Just a few short questions:

    I have to define dynamic equilibrium state in terms of a) reaction rates b) change in observable properties and c) energy and entropy state

    I also have to explain in which of the following closed containers has the greatest vapour pressure.
    the choices are a) 1L container with 5mL of water held at 20degreescelcius
    b) 2L container with 15mL of water held at 30degcel
    c) 3L containter with 500mL at 25degcel

    finally, ethanol and water are completely miscible; that is, they dissolve in each other in all propertions:
    a) when the two substances are mixed, is randomness increased or decreased?
    b) heat is liberated in the dissolving process. Does the tendency towards minimum energy favour the seperated pure substances, or the solution of one in the other?
    c) In view of the tendicies listed in a) and b) above, explain why water and ethanol are completley miscible.

    Thanks for the help.
  2. jcsd
  3. Mar 4, 2005 #2


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    a)The ratio of the rate constants of forward relative to reverse reaction describes K, you'll need to find the details yourself within your text. b)The observable properties...basically relating to when the rate of the forward and reverse reaction are equal (note that I'm referring to rate not rate constant), other than that I'm not quite sure what they're referring to. c) Find a derivative of the free energy Gibbs equation that relates to the rate constnat...free energy of the reaction is zero at equilibrium.

    use PV=nRT

    a)I would say it decreases, the solutions becomes ordered as water molecules allign themselves and interact with ethanol molecules.
    b)This seems to be a case where the entropy aspects of the reaction make it favorable even when it is somewhat unfavorable in terms of enthalpy.
    c)Observe b)
  4. Mar 20, 2005 #3
    for that second question..how do I get the n variable, to figure out hte pressure in PV=nRT?

  5. Mar 27, 2005 #4
    for a) although the water molecules are aligning themselves with the ehtanol molecules isnt the whole point of a miscable substance based on the fact that the randomness of the system increases allowing the two substances to become completely miscible with one another?

    for b) since the general entropy of the system is increasing when the substances are mixed wouldnt that mean that the enthalpy (or tendency toward minimum energy) favours the separated pure substances?

    and for c) we can explain that water and ethanol are completely miscible since an equilibrium has formed between the systems drive toward minimum energy and the drive toward maximum randomness?
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