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 coffec Thermometer cup calorimcter. Cardboard or Styrofoam lid In the laboratory a general chemistry student finds that when 4.37 g of NH4CIO4(s) are dissolved in 105.40 g of water, the tempcrature of the solution drops from 23.72 to 20.65 °C The heat capacity of the calorimeter (sometimes referred to as thc calorimeter constant) was determined in a scparatc cxpcriment to bc Nested Styrofoam cups .57 J/oC Based on the student's observation, calculate the enthalpy of dissolution of NH4CIO4(s) in kJ/mol Assume the specific heat of the solution is cqual to the specific heat of water. AHdissolution = Reaction occurs in solution. kJ/mol Submit Answer Retry Entire Group 9 more group attempts remaining

Explanation / Answer

The 4.37-g of NH4ClO4 caused the temperature of the 105.40-g of water to increase by (23.72 oC – 20.65 oC)3.07 oC. In addition to the water, the calorimeter also gained heat at the rate of 1.57-J/ oC.

Heat gained = [105.40-g x 3.07 oC x 4.184-J/g*oC] + [1.57J/oC x 3.07 oC]

= 1353.85-J + 4.8199 -J = 1349.0301 -J

This quantity of heat was released by 4.37-g of NH4ClO4.

Now calculate the number of moles as follows:

4.37-g of NH4ClO4 / molar mass

= 4.37-g of NH4ClO4 /117.4891 g/mol = 0.0372 mol

Enthalpy of dissolution : 1349.0301 -J /0.0372 mol

= 36264.25-J = 36.26 -kJ/mol

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