Thermodynamic question

  1. (20 points) A container of liquid salt bath is used as a calorimeter to determine the enthalpy of formation of FeSi. It has been determined by experiment that the heat capacity of the bath is 5000J/K at 600°  With the bath originally at 600°C, the following experiments are performed.
  1. A mixture of 0.1 mole of pure Fe and 0.1 mole of pure Si at 25°C is dropped into the calorimeter.  When the mixture has dissolved completely, the temperature of the bath is found to have increased 0.275°C from 600°C.
  2. 0.1 mole of formula of FeSi (0.2 mole of atoms) at 25°C is dropped into the calorimeter.  When the compound is dissolved completely, the temperature of the bath decreases by 1.295°C from 600°C.

Answer the following questions

  1. Calculate the weights of pure Fe, pure Si, and the compound FeSi from their moles used in the experiments. (2 points)
  2. What are the enthalpies of formation of FeSi in per moles of formula and per mole of atoms, respectively? (9 points)
  • To what temperature does the result of the enthalpy of formation apply? Explain. (9 points)

 

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  1. (A bonus problem, 5 points) Define the first-order and second-order phase transformations.

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