When a solid dissolves in water, heat may be evolved or absorbed. The heat of di

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 15.26 g of BaBr2(s) are dissolved in 112.00 g of water, the temperature of the solution increases from 25.62 to 27.96 °C.

The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.56 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.

Explanation / Answer

The 15.26g of BaBr2 caused the temperature of the 112.00-g of water to increase by (25.62 to 27.96 °C) 2.34 oC.

And water, the calorimeter also gained heat at the rate of 1.56-J/ oC.
Heat gained = [112-g x 2.34 oC x 4.184-J/g oC] + [1.56J/oC x 2.34 oC]
= 1097+ 3.65= 1100.65 J

This quantity of heat was released by 15.26-g of BaBr2 = 15.26-g /297.14 g = 0.05136 mol
Enthalpy of dissolution: 1100.65-J/0.05136 mol

= 21430 J Or

= 21.43 kJ/mol

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