Calculate the partial molar enthalpy of solute. Please help. thank you. ?

The enthalpy change accompanying the dissolution of a solute B in 1000 g water is dependent on the number of moles (n) of B dissolved. The relationship of the enthalpy change deltaH to the mol B (n) is expressed by the equation

deltaH = 40 n + 30 n^2

Calculate the partial molar enthalpy of the solute B for a 0.01 molal solution. The answer should be 40.6

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1 Answer

  • 2 months ago

    Delta H = 40 n + 30 n^2 

    where n = moles dissolved in 1 kg water

    0.01 molal solution means 0.01 mol dissolved in 1 kg water, to n = 0.01

    Delta H = 40 (0.01) + 30 (0.01)^2

    Delta H = 0.403 

    Obviously this is not the answer you have given. Using the answer you were given, you can work this problem in reverse to calculate what n would be:

    40.6 = 40n + 30n^2

    30n^2 + 40 n - 40.6 = 0

    Using the quadratic formula to solve for n gives a positive root of n = 0.674. 

    So, there is obviously an issue with this question, and you should talk to your instructor or TA about it.

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