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Homework Help: Thermodynamics/ Humdifier

  1. Nov 4, 2016 #1
    1. The problem statement, all variables and given/known data

    A certain humidifier operates by raising water to the boiling point and then evaporating it.
    Every minute 30 g of water at 20◦ C are added to replace the 30 g that are evaporated. The
    heat of fusion of water is 333 kJ/kg, the heat of vaporization is 2256 kJ/kg, and the specific
    heat is 4190 J/kg · K. How many joules of energy per minute does this humidifier require?
    A. 3.0 × 104
    B. 8.8 × 104
    C. 7.8 × 104
    D. 1.1 × 105
    E. 2.0 × 104
    2. Relevant equations

    3. The attempt at a solution

    energy per minute = (energy needed to heat water to boiling point) + (energy needed to convert liquid water to gas at the boiling point)

    E = (30 g)(4.190 J/g-°C)(100 - 20°C) + (30 g)(2256 J/g)
    E = 7.8e4 J but the correct answer is B?????
  2. jcsd
  3. Nov 4, 2016 #2


    User Avatar

    Staff: Mentor

    I get the same answer as you.
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