When a solid dissolves in water, heat may be evolved or absorbed. The heat of di

Question

When a solid dissolves in water, heat may be evolved or absorbed. The heat of dissolution (dissolving) can be determined using a coffee cup calorimeter. In the laboratory a general chemistry student finds that when 8.88 g of N_aCIO_4(s) arc dissolved in 10S.80 g of water, the temperature of the solution drops from 24.46 to 21.90 degreeC. The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.72 J/degreeC. Based on the student's observation, calculate the enthalpy of dissolution of NaCIO_4(s) in kj/mol. Assume the specific heai of the solution is equal to the specific heat of water.

Explanation / Answer

No of mol of NaClO4 = 8.88/122.44 = 0.0725 mol

mass of solution = 8.88+105.8 = 114.68 grams

heat absorbed = 114.68*4.18*(24.46-21.9)+ (24.46-21.9)*1.72

    = 12.31 kjoule.

enthalpy of dissolution = 12.31/0.0725 = 169.79 kj/mol

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