AP Chemistry
6.6 Introduction to Enthalpy of Reaction
6.4 Heat Capacity and Calorimetry
A student conducts a calorimetry experiment to determine the standard molar enthalpy of reaction, \(\Delta H_{\text{rxn}}^\circ\), for the exothermic dissolution of calcium chloride:
\[ \text{CaCl}_2\text{(s)} \rightarrow \text{Ca}^{2+}\text{(aq)} + 2\,\text{Cl}^-\text{(aq)} \]
The student dissolves \(5.55\text{ g}\) of \(\text{CaCl}_2\text{(s)}\) (\(0.0500\text{ mol}\)) in \(100.0\text{ g}\) of distilled water in a coffee-cup calorimeter. The student delays placing the lid on the calorimeter, allowing a significant amount of heat to escape to the surroundings before the maximum temperature of the solution is recorded. Which of the following correctly describes the effect of this error on the calculated \(\Delta H_{\text{rxn}}^\circ\) and identifies an appropriate procedural modification to minimize this error in future trials?
\[ \text{CaCl}_2\text{(s)} \rightarrow \text{Ca}^{2+}\text{(aq)} + 2\,\text{Cl}^-\text{(aq)} \]
The student dissolves \(5.55\text{ g}\) of \(\text{CaCl}_2\text{(s)}\) (\(0.0500\text{ mol}\)) in \(100.0\text{ g}\) of distilled water in a coffee-cup calorimeter. The student delays placing the lid on the calorimeter, allowing a significant amount of heat to escape to the surroundings before the maximum temperature of the solution is recorded. Which of the following correctly describes the effect of this error on the calculated \(\Delta H_{\text{rxn}}^\circ\) and identifies an appropriate procedural modification to minimize this error in future trials?
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