Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Thermodynamics ice cube question

  1. Jan 24, 2009 #1
    1. The problem statement, all variables and given/known data
    How much energy is required to change a 40.0 g ice cube from ice at -8.0°C to steam at 108°C?


    2. Relevant equations
    q=mct


    3. The attempt at a solution
    i remember one of our TAs going over something like this a long time ago..I think i have to like add up all the energies from the ice going to like 0 C then to like 100C and then 108 C??

    can someone help me out
     
  2. jcsd
  3. Jan 24, 2009 #2
  4. Jan 24, 2009 #3
    ok tell me if im correct
    add up all the energy from ice going from -8 to 0
    0 to 100 and then 100 to 108?

    am i even close?
     
  5. Jan 24, 2009 #4
    Yes, you are. Now you have to also consider the energy required to change phase (ice to water, water to steam).
     
  6. Jan 24, 2009 #5
    umm im not sure what that means
     
  7. Jan 28, 2009 #6
    Consider: http://www.splung.com/heat/images/latentheat/phasechange.png and also the URL I gave you in my first post.

    We separate this problem into stages:

    Energy is required to raise the temperature of the solid, in this case the ice, from -8 to 0 degrees celcius. This is stage A-B.

    Energy is then required to change phase from ice to water. At this point the temperature remains the same. This is stage B-C.

    Once again, energy is required to raise the temperature from 0 to 100 degrees celcius. This is stage C-D.

    The water then changes state again to steam. This is another phase change. This is stage D-E.

    Finally, the temperature of the steam is raised by 8 degrees to 108 degrees celcius. This is stage E-F.

    So, to calculate the energy required to raise 40g of ice from -8 to 108 degrees celcius we must use two equations. One to calculate the energy required to change phase at stages B-C and D-E, and another to calculate the energy required to raise the temperature at stages A-B, C-D and E-F.

    The latent heat equation is:

    [tex]Q=mL[/tex]

    and the other equation required is the one you've already specified.
     
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook