When a solid dissolves in water, heat may be evolved or absorbed. The heat of di
ID: 502874 • Letter: W
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 18.11 g of BaBr2(s) are dissolved in 105.50 g of water, the temperature of the solution increases from 23.71 to 26.57°C.
The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.90 J/°C.
Based on the student's observation, calculate the enthalpy of dissolution of BaBr2(s) in kJ/mol.
Assume the specific heat of the solution is equal to the specific heat of water.
Hdissolution = ______ kJ/mol
Explanation / Answer
heat absorbed by solution,
Qsolution = Ccal*delta T + mw*Cw*delta T
= 1.90*(26.57 - 23.71) + 105.50 * 4.184*(26.57 - 23.71)
= 5.434 + 1262.4
=1267.8 J
mol of BaBr2 = mass of BaBr2 / molar mass of BaBr2
= 18.11 / 297.14 g/mol
= 0.06095 mol
Hdissolution = -Qsolution/mol
= -1267.8 J / 0.06095 mol
= -20801 J/mol
= -20.8 KJ/mol
Answer: -20.8 KJ/mol
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