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8 September, 23:10

When 0.876 g of CaCl2 (110.98 g/mol) is added to 95.0 g of water at 22.4 °C in a 'coffeecup' calorimeter, the temperature of the resulting solution increases to 29.7 °C. The specific heat capacity of the solution is 4.184 J/°C·g and the heat capacity of the Styrofoam cup is negligible. A) Is this reaction endothermic or exothermic? How do you know? B) Calculate the molar heat of solution (∆Hrxn) of CaCl2 in water.

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  1. 8 September, 23:23
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    a) the reactionis exothermic

    b) The molar heat of solution is 367 kJ/mol

    Explanation:

    Step 1: Data given

    Mass of CaCl2 = 0.876 grams

    Molar mass of CaCL2 = 110.98 g/mol

    Mass of water = 95.0 grams

    Initial temperature of water = 22.4 °C

    Final temperature of water = 29.7 °C

    Specific heat capacity = 4.184 J/g°C

    Since the temperature increases, heat was generated or given off by the reaction. This means the reaction is exothermic.

    B) Calculate the molar heat of solution (∆Hrxn) of CaCl2 in water.

    q = m*c*∆T

    with m = the mass = 95 grams

    with c = the specific heat capacity = 4.184 J/g°C

    with ∆T = The change in temperature = T2 - T1 = 29.7 - 2.4 = 7.3

    q = 95 * 4.184 * 7.3 = 2.9 kJ

    Calculate number of moles of CaCl2

    Moles CaCl2 = Mass CaCl2 / Molar mass CaCl2

    Moles CaCl2 = 0.876 grams / 110.98 g/mol

    Moles CaCl2 = 0.0079 moles

    Molar ∆Hrxn = 2.9 kJ / 0.0079 moles = 367 kJ/mol

    The molar heat of solution is 367 kJ/mol
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