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Thermodynamic Work

  1. Oct 4, 2009 #1
    1. Five moles of an ideal monatomic gas with an initial temperature of 124*C expand and, in the process, absorb an amount of heat equal to 1140J and do an amount of work equal to 2200J . What's the final temperature



    2. Q=m1.5R delta T



    3. I tried adding 1440 to 2200 as Q and solving for T final but that doesnt work help?
     
  2. jcsd
  3. Oct 4, 2009 #2

    Andrew Mason

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    This is a first law problem. Q=m1.5R delta T only works at constant volume. But you know that this is not a constant volume process - [how?].

    Write out the first law. You are given the heat flow, dQ and the work, PdV, so what is the change in internal energy? Then you can determine the temperature from the change in internal energy.

    AM
     
  4. Oct 4, 2009 #3
    First of all what is dQ, do you want me to integrate something im not given a function? or is there another differential so that i can take the derivative of a function if so what function? you said im given the heat flow does that mean i take the integral of 1140 and get 1140Q? then what am i supposed to do with that? because dQ = Q'(t)dt. I'm not given a function... i don't understand. please tell me what formula i use?
     
  5. Oct 5, 2009 #4

    Andrew Mason

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    The formula you use is the first law of thermodynamics. Write out the first law as it applies to the thermodynamic system ie. the gas. You are given dQ. dQ is the heat flow into/out of the gas. You are given dW. dW is the work done by the gas. Plug those into the first law an that gives you dU. It is that simple.

    Once you have found the change in internal energy, you can find the change in temperature. What is the relationship between change in internal energy and temperature?

    AM
     
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