Aim: How to measure molar heat of solution

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A student performed an experiment in which she dissolved a salt in water. She took the initial temperature of the water, before dissolution of the salt, to be 23oC. After the salt was completely dissolved in the water the temperature of the solution dropped to 19oC. Was the dissolution of the salt and exothermic or endothermic process? Explain.

Calorimetry

•Calorimetry is the measurement of heat flow into or out of a system for chemical or physical processes.• In calorimetry, the heat released by a system is equal

to the heat absorbed by its surroundings. Conversely, the heat absorbed by the system is equal to the heat released by the surrounding.•http://

highered.mheducation.com/sites/9834092339/student_view0/chapter48/bomb_calorimeter.html

Heat of SolutionThe Heat of Solution is the amount of heat energy absorbed (endothermic) or released (exothermic) when a specific amount of solute dissolves in a solvent. Molar heat of solution is the amount of energy absorbed or released per one mole of the solute.

Substance Heat of Solution (kJ/mol)

NaOH -44.51NH4NO3 +25.69

KNO3 +34.89

HCl -74.84

Problem 1

In an experiment, a student added 1.01 grams of lithium bromide, LiBr, to 12.21 grams of water at 20.1°C. After stirring for awhile, the temperature of the mixture rose to 31.3°C. Given this information, we can calculate the molar heat of solution for lithium bromide.

Problem 2A calorimeter was used to determine the molar enthalpy of a solution of AlCl3. When a sample of AlCl3 was dissolved in water the following data were collected.

Determine the molar heat (kJ/mol) of solution.

Mass of AlCl3 (g)

Mass of H2O (g)

Initial Temp. (oC)

Final Temp. (oC)

10.0 250.0 20.0 46.3