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March 26, 2017

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Given that the specific heat capacities of ice and steam are 2.06 J/g°C and 2.03 J/g°C, the molar heats of fusion and vaporization for water are 6.02 kJ/mol and 40.6 kJ/mol, respectively, and the specific heat capacity of water is 4.18 J/g°C, calculate the total quantity of heat evolved when 20.6 g of steam at 216°C is condensed, cooled, and frozen to ice at -50.°C.

  • chemistry - ,

    The easiest way to do this is in parts. It's easier to understand.
    q1 = heat to move steam from 216 to 100.
    q1 = mass steam x specific heat steam x delta T.

    q2 = heat to condense steam at 100 C to liquid water at 100 C.
    q2 = mass steam x heat vaporization

    q3 = heat to move liquid water from 100 C to 0 C.
    q3 = mass x specific heat water x delta T.

    q4 = heat to freeze liquid water at 0 C to ice at 0 C.
    q4 = mass water x heat fusion.

    q5 = heat to move ice from 0 C to -50 C.
    q5 = mass x specific heat ice x delta T.

    total heat evolved = q1 + q2 + q3 + q4 + q5 = ??
    Watch the units. I would make sure everything was done in joules.

  • chemistry - ,

    Another note: You must change grams to moles for the mass if using J/mole or change J/mole to J/g if you want to use mass in grams.

  • chemistry - ,

    is the correct answer 68.93kJ?

  • chemistry - ,

    I worked it through and obtained 68.89 (the difference probably is rounding) kJ which I would round to 68.9 kJ (3 s.f. is all we are allowed) and your answer would be rounded to 68.9 kJ.

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