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Chemistry LibreTexts

3.6.1: Practice Heat to Melt or Boil

  • Page ID
    235923
  • Exercise \(\PageIndex{1}\)

    How much heat does it take to melt 43.77 g of copper if the copper is already at its melting point?  The heat of fusion of copper is 49 cal/g.

    Answer

    2100 cal  (2144.73 rounded to 2 sig. dig.)

     

    Exercise \(\PageIndex{1}\)

    How much heat does it take to boil 26.88 g of ethanol if the ethanol is already at its boiling point?  The heat of vaporization of ethanol is 853 J/g.

    Answer

    22900 J

     

    Exercise \(\PageIndex{1}\)

    What if you start with 85.5 g of ethanol that is only 18.5 °C?  The boiling point of ethanol is 78.4 °C. The heat of vaporization of ethanol is 853 J/g. The specific heat of ethanol is 2.46 J/g°C.

    Answer

    85500 J (It takes 12600 J to heat it from 18.5°C to 78.4°C plus another 72900 J to boil it.)

     

    Exercise \(\PageIndex{1}\)

    Starting with 245 g of ice that is –16.3°C, how much energy is needed to warm the ice, melt it, and warm the water to 27.2 °C? 

    The specific heat of ice is 0.488 cal/g°C, the specific heat of liquid water is 1.00 cal/g°C, and the heat of fusion of ice is 79.7 cal/g.

    Answer

    28100 cal (It takes 1950 cal to warm the ice to 0.0°C, plus 19500 cal to melt the ice, plus 6660 cal to warm the water to 27.2°C).

     

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