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Homework Help: Heat Capacity

  1. Oct 8, 2009 #1

    I need help for number 2(b)

    A student investigates the evaporation of water. He pours 100 cm3 of water into measuring
    cylinder A and 100 cm3 of water into measuring cylinder B. Measuring cylinder A is kept
    at 40 °C and B is kept at 80 °C in the same part of the laboratory. Fig. 2.1 shows the two
    measuring cylinders after 3 days.

    The specific latent heat of vaporisation of water is 2300 J / g and the density of water is
    1.0 g / cm3. During the three days, the water level in B drops from the 100 cm3 mark to
    the level shown in Fig. 2.1. Calculate the energy used to evaporate water from B during
    the three days.

    Volume = (80-60) = 20 cm3

    1 cm3 = 1 g
    20 cm3 = 20 g

    Q= ml
    Q= 20/1000 x 2300
    = 46(Not the right answer)

  2. jcsd
  3. Oct 8, 2009 #2


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    Homework Helper

    I see 2 difficulties.
    First, the 20 grams should not be converted to kg because the latent heat "2300 J / g" is in grams, not kg.

    Second, I think you have to add the heat required to warm the 20 g up to 100 degrees.
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