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    lisanoce's Avatar
    lisanoce Posts: 30, Reputation: 1
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    #1

    Jun 15, 2009, 02:51 PM
    Molar enthalpy.finding final temperature
    The molar enthalpy of solution of ammonium chloride is +14.8 KJ/mol. What would be the final temperature of a solution in which 37.5 grams of ammonium chloride is added to 200.0 mL of water, initially at 25.0 degrees Celsius? I had trouble with this on a test so I need help correcting it. Thanks
    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #2

    Jun 16, 2009, 08:58 AM

    First, write the equation. You should do it for every reaction, until you can view them mentally.

    NH4Cl(s) --> NH4+(aq) + Cl- (aq) (Enthalpy = +14.8 kJ/mol)

    Find the number of moles of NH4Cl that dissolves. Multiply that by the enthalpy of solution of the reaction.

    Now, use



    where Q is the amount of heat involved, m the mass of water, c the specific heat capacity of water (4.3 J/(gK))

    Find the temperature change, theta.

    Since initial temperature is 25 C, subtract theta from 25, and that's your estimated final temperature.

    Of course, if you did the experiment, you won't have that temperature since the system can absorb heat from the surroundings.
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