Question 15

A student carries out an experiment to determine the enthalpy change of solution when anhydrous calcium chloride dissolves in water.

The student uses $g150\text{ g}$ of water. The thermometer readings before and after adding the anhydrous calcium chloride are:

Temperature before adding anhydrous calcium chloride: $20.2∘C20.2^\circ\text{C}$
Temperature after adding anhydrous calcium chloride: $26.8∘C26.8^\circ\text{C}$

Calculate the temperature change in $∘C^\circ\text{C}$ .

Calculate the heat energy change, in joules, using the expression:

\text{heat energy change (J)} = \text{mass of water (g)} \times 4.2 \times \text{temperature change (}^\circ\text{C)}

The student used $g5.55\text{ g}$ of anhydrous calcium chloride. Calculate the amount, in moles, of anhydrous calcium chloride dissolved ( $CaCl2=111M_r\text{ of CaCl}_2 = 111$ ).

Calculate the molar enthalpy change, in $kJ/mol\text{kJ/mol}$ , for dissolving anhydrous calcium chloride. Since the temperature increased, include the appropriate sign ( $+$ or $-$ ) with your value.