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Homework Help: Latent Heat Question

  1. Apr 23, 2014 #1
    1. The problem statement, all variables and given/known data

    A scientist heats up a substance by applying heat at a constant rate of 75 J/s. She measures that
    it takes 1 minute for 100 grams of the substance to evaporate. What is the latent of vaporization
    of this substance? If she starts with 1 kg of the substance, how long will it take for it to
    evaporate and how much energy will it take to evaporate the substance?

    2. Relevant equations


    3. The attempt at a solution[/b

    I'm not really sure how to use Q=mL. Does 75 J/s go into Q or is Q the total amount of joules. I know m is the mass and L is the specific latent heat.
  2. jcsd
  3. Apr 23, 2014 #2


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    I will use the formula ##E=mL_v## for easiness.
    J/s is the unit of power so if you know the power and the time,you should be able to find the energy supplied.
    Use##E=mL_v## to find the ##L_v##.
  4. Apr 23, 2014 #3
    So, 75 x 60 is equal 4500. 4500= (.1kg)(L) -> L=45000. If it takes 1 minute to vaporize 100g it should take 10 minutes for a kg and 45000 J?
  5. Apr 23, 2014 #4


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