You need to find the abundance. Then, multiply the abundance by 100, and add that to the mass for each isotope. Basically, for each isotope, take the percentage abundance and add it to the mass. Multiply each calculation of these together to get your average atomic mass,
<h2>Answer:</h2>
<em>8.67kJ/mol</em>
<h2>Explanations</h2>
The formula for calculating the amount of heat absorbed by the water is given as:

Determine the moles of KI

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

Determine the enthalpy of solution in kJ•mol-1

Hence the enthalpy of solution in kJ•mol-1 for KI is 8.67kJ/mol
There are two possible situations.
1) If a phase change is not occurring, then the heat added contributes to increased translational energy of the particles. What that means is the particles move/vibrate faster.
2) If a phase change is occurring, then the heat added contributes to the breaking of bonds or intermolecular forces (depending on the chemical nature of the matter you're dealing with).
The number of Atoms must be the same on both sides