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    Asoom's Avatar
    Asoom Posts: 52, Reputation: 1
    Junior Member
     
    #1

    May 10, 2009, 06:23 AM
    Thermochemistry
    Could anybody help me in this HW


    A piece of metal weighing 5.10g at a temperature of 48.6C was placed in a calorimeter into 20mL of water at 22.1C ,and the final equilibrium temperature was found to be 26.8C
    What is the specific heat of the metal ?


    When a 3.25g sample of solid sodium hydroxide was dissolved in a calorimeter in 100g of water , the temperature rose from 23.9C to 32C . Calculate △H (in KJ/mol NaOH) for the solution process:

    NaOH ........> Na^+ + OH^-

    Assume it's a perfect calorimeter and that the specific heat of the solution is the same as that of pure water


    Describe how you could determine the specific heat of a metal by using the apparatus and techniques in this experiment
    Unknown008's Avatar
    Unknown008 Posts: 8,076, Reputation: 723
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    #2

    May 10, 2009, 08:42 AM

    I did that in Physics, the formula relating mass, energy, specific heat capacity and temperature change is:



    Since the energy involved is the same, then,

    , taking the subscripts of 1 as those for the metal and the subscript of 2 for water.













    Solve for c_1, which will be in J/(gK), convert into J/(kgK) by multiplying by 1000.

    For the next one, find firstly the number of moles in your NaOH sample. You'll see you answer should be in KJ/mol, obviously, you have to convert 3.25 g of NaOH to moles.

    Using the same formula, you can find the energy actually required to make the temperature of 100g of water raise from 23.9 Celsius to 32 Celsius.



    Put the values for water, to find Q, the energy that water absorbs. That energy equals to the amount of energy released by the dissociation of NaOH. Therefore, that amount of moles of NaOH gave that amount of heat. Can you find the amount of heat released per mole of NaOH now?

    The last question is done through the first question you had. You can put in more details like the experiment was carried out several times to obtain a more accurate result and some other details you usually find in physics questions.

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