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Homework Help: A thermal physics question about steam and coffee, please could you help?

  1. Oct 17, 2012 #1
    1. The problem statement, all variables and given/known data
    A coffee machine in a café passes steam at 100°C into 0.18kg of cold coffee (s.h.c. the same as that of water(4200j/kg/K)) to warm it. If the initial temperature of the coffee is 14°C, what mass of steam must be supplied to raise the temperature of the coffee to 85°C

    2. Relevant equations
    E = mcΔθ
    possibly E = ml ????

    3. The attempt at a solution
    I have thought.
    E = mcΔθ
    = (0.18)(4200)(71)
    = 53676J
    so 53676J of energy is needed to increase the temperature of the cold coffee from 14°C to 85°C

    OK so the steam is at 100°C so it is at 373.15K
    how can I use the temperature of the steam to find out how much steam would be needed to increase the temperature of the cold coffee to 85°C?
    Would the steam need to be condensed?
    How could i go about finding out how much energy a unit of mass of steam would have?
  2. jcsd
  3. Oct 18, 2012 #2
    Yes, you need to condense the steam. Look up the heat of vaporization of water at its normal boiling point 100C.
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