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Homework Help: Espresso Problem

  1. Jan 30, 2010 #1
    I am having trouble with this question:

    The temperature of the espresso coffee (mostly water) can be increased by blowing 100 C steam into it. How much steam (in grams) is needed to heat up a 20 cm^3 cup of espresso from 50 C to 80 C? What is the volume of this quantity of steam assuming that the steam is an ideal gas?

    So far I have started like so:

    Since the 20 cm^3 conversion to grams with water is just 1:1 I just said 20 g of water for starting.

    And approached it like so:

    (20g)(1 g/cal)(80 C – 50 C)= -ms(-540 cal/g) + (1 cal/g)(80 C – 100 C) and got ms to be roughly 1.11 g of steam.
     
  2. jcsd
  3. Jan 30, 2010 #2

    mgb_phys

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    Don't know the numbers for cal off by heart but that's the right approach

    mass coffee * specific heat cap * temp change = energy (steam->water) + mass steam * specific heat cap water * temp change (from 100 to final T)
     
  4. Jan 31, 2010 #3
    my approach is

    mass of coffee*specific heat of water(1cal/g/K)*delta T= mass of steam * heat of condensation(540cal/g)+mass of steam * 1cal/g/K* (100-final T)

    and the hw software determined that I am wrong

    HELP!!!! due tomorrow 10 am
     
  5. Jan 31, 2010 #4
    help!!!!!!!!!!!!!!!!!!!
     
  6. Feb 1, 2010 #5
    anyone?
     
  7. Feb 1, 2010 #6

    Redbelly98

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    It may be too late to help you, but here is some advice for the future:

    Show what answer you got. You have set up the correct equation, so we can't tell where your mistake is.

    This forum has people from all over the world, from many different time zones. We don't know when "10 am" is for you.

    Don't bump your thread every couple of hours.
     
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