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When 1.50 g of calcium chloride is dissolved in 150.0 g of water, the temperature of the water rises from 20.50°C to 22.25°C. Assume that all the heat is absorbed by the solution.
(a) Calculate the heat of solution per gram and per mole of CaCl2 that dissolves.
(b) Is this an exothermic or an endothermic process?
(c) Determine the mass of calcium chloride required to prepare the hot compress with the following characteristics:
(i) maximum temperature of 15.0°C above average body temperature
(ii) contains 100.0 g of water

Can you please explain too, thank you

  • chemistry - ,

    a) q = mass H2O x specific heat H2O x (Tfinal-Tinitial) = about 1100 J but you need to do it more accurately.
    heat soln per gram = 1100/1.5g = ?
    heat soln pr mol = (1100/1.5) x molar mass CaCl2.
    b) Water temperature goes up so it is being heated; therefore, CaCl2 dissolving in water is an exothermic reaction.
    c)I would do this.
    How many joules do you want? I'm a little confused about the temperature but if we want 15 degrees above body temperature that would be about 37 for body T + 15 = about 52 for Tfinal. What do we pick for Tinitial. I don't know the answer to that and the problem doesn't help; however, I assume we might consider that the soln would be at room temperature (say 25C) before the solution was applied to the patient. So we will need
    q = 100 g water x specific heat water x (52-25) = about 11,000 J (again you need it more accurately),
    So how many grams will we need. If we can get 1100 from 1.5 g, we will need
    1.5 x (11,000/1100) = about 15 g for 11,000 J. Check my thinking. Check my work.

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