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 2.06 g of CaCl2(s) are dissolved in 117.70 g of water, the temperature of the solution increases from 23.22 to 26.33 °C.

The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.64 J/°C.

Based on the student's observation, calculate the enthalpy of dissolution of CaCl2(s) in kJ/mol.

Assume the specific heat of the solution is equal to the specific heat of water.

?Hdissolution = ______kJ/mol 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 2.06 g of CaCl2(s) are dissolved in 117.70 g of water, the temperature of the solution increases from 23.22 to 26.33 °C.

The heat capacity of the calorimeter (sometimes referred to as the calorimeter constant) was determined in a separate experiment to be 1.64 J/°C.

Based on the student's observation, calculate the enthalpy of dissolution of CaCl2(s) in kJ/mol.

Assume the specific heat of the solution is equal to the specific heat of water.

?Hdissolution = ______kJ/mol

Explanation / Answer

Snce temperature is increased, it evolves heat and the dissolution is exothermic.

Heat change = mass * specific heat * change in temperature + heat capacity of calorimeter * change in temperature

q = 117.70 * 4.184 * (26.33 - 23.22) + 1.64 * (26.33 - 23.22)

q = 1536.6 J

Mass of CaCl2 = 2.06 g.

Molar mass of CaCl2 = 40 + 2 (35.5) = 111 g/mol

Moles of CaCl2 = mass / molar mass = 2.06 / 111.0 = 0.0186 mol

Enthalpy of dissolution = - q / n

deltaH = - 1536.6 / 0.0186

deltaH = - 82797 J/mol

deltaH = - 82.8 kJ/mol

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