Question

When 20.0 g of KI are dissolved in 50.0 mL of distilled water in a calorimeter, the temperature drops from 24.0 °C to 19.0 °C. Calculate the enthalpy of solution in kJ•mol-1 for KI.

Answer 1

8.67kJ/mol

Explanations

The formula for calculating the amount of heat absorbed by the water is given as:

`\begin{gathered} q=mc\triangle t \\ q=50*4.18(J)/(g^oC)*(19-24) \\ q=50*4.18*(-5) \\ q=-1045Joules \\ q=-1.045kJ \end{gathered}`

Determine the moles of KI

`\begin{gathered} moles\text{ of KI}=\frac{mass\text{ of KI}}{molar\text{ mass of KI}} \\ moles\text{ of KI}=\frac{20g}{166g\text{/mol}} \\ moles\text{ of KI}=0.1205moles \end{gathered}`

Since heat is lost, hence the enthalpy change of the solution will be negative that is:

`\begin{gathered} \triangle H=-q \\ \triangle H=-(-1.045kJ) \\ \triangle H=1.045kJ \end{gathered}`

Determine the enthalpy of solution in kJ•mol-1

`\begin{gathered} \triangle H_(diss)=(1.045kJ)/(0.1205mole) \\ \triangle H_(diss)\approx8.67kJmol^(-1) \end{gathered}`

Hence the enthalpy of solution in kJ•mol-1 for KI is 8.67kJ/mol