When a 5.00 g sample of KBr is dissolved in water in a calorimeter that has a total heat capacity of 3.10 kJ ⋅ K - 1, the temperature decreases by 0.270 K. Calculate the molar heat of solution of KBr.

19.9J/mol

Explanation:

Using the law of conservation of energy, the heat of solution of KBr equals the heat absorbed or released by the calorimeter.

In this case, the temperature of the calorimeter decreased, then it released heat that the sample of KBr absorbed. This is, then, an endothermic change.

The heat released by the calorimeter equals its heat capacity multiplied by the change in temperature:

Heat released = 3.10 kJ. K⁻¹ * 0.270 K = 0.837J

Then:

Heat absorbed by the sample of KBr = 0.837J

The molar heat of solution is the heat absorbed by the sample divided by the number of moles in the sample.

Convert 5.00 g of KBr into number of moles

number of moles = mass in grams / molar mass number of moles = 5.00g / 119.002 g/mol = 0.042016 mol

Divide the heat absorbed by the number of moles

Molar heat of solution = 0.837J / 0.042016 = 19.92 J/mol

You must round to 3 significant figures: 19.9J/mol ← answer