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20.0 g of ammonium nitrate (NH4NO3) is dissolved in 125 g of water in a coffee-cup calorimeter, the temperature falls from 296.5 K to 286.4 K. Find the value of q for the calorimeter.

  • chemistry - ,

    When NH4NO3 is dissolved in water, it dissociates into its ions, followed by a temperature drop:
    NH4NO3 -> NH4+ + NO3-
    (though it's not really that relevant though ^^;)

    Anyway, the heat gained or lost can be calculated using the formula
    Q = mc(T2 - T1)
    m = mass (grams)
    c = specific heat capacity (J/g-K)
    T = temperature (K)

    Here, we'll use an assumption that the specific heat of the solution is equal to that of water, which is c = 4.184 J/g-K.
    The total mass of solution is 20 + 125 = 145 grams.
    Q = (145)*(4.184)*(286.4 - 296.5)
    Q = -6127.47 J
    The Q negative because heat is released in the dissociation.

    Check the significant figures.
    Hope this helps :3

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