91Ó°ÊÓ

Calorimetry is a technique used to measure the heat absorbed or released during a chemical or physical process. This experimental method helps us understand the energy changes that accompany reactions. In the context of our exercise, a calorimeter is used to measure the heat change when calcium chloride (\( CaCl_2\)) dissolves in water.

To carry out a calorimetry experiment, you need to know a few key components:

• The initial and final temperatures of the solution
• The heat capacity of the calorimeter and its contents
• Amount of substance being tested (in this case, calcium chloride)

By measuring these, you can calculate heat transfer, expressed as \( q \), using the formula:\[ q = C \cdot \Delta T \]where \( C \) is the heat capacity and \( \Delta T \) is the change in temperature.

Dissolution of calcium chloride is a common process studied in chemistry due to its interesting thermal effect. When calcium chloride (\( CaCl_2\)) dissolves in water, it dissociates into its ions:\[ CaCl_2(s) \rightarrow Ca^{2+}(aq) + 2Cl^{-}(aq) \]

This process is exothermic, meaning it releases heat. The exothermic nature of this reaction is evidenced by the increase in temperature observed in the calorimeter. When 23.6 grams of calcium chloride are dissolved, the temperature of the solution rises, which we measure and analyze through calorimetry to find the enthalpy change. This is an important parameter, as it indicates how much heat is exchanged with the surroundings when a mole of the compound dissolves.

Heat transfer is the movement of thermal energy from one object or substance to another. In our exercise, heat is transferred from the calcium chloride solution to the surrounding water in the calorimeter.

By calculating the change in the solution's temperature (\( \Delta T = 13.7^{\circ} \text{C}\)), and knowing the heat capacity (\( 1258 \,\text{J}/^{\circ}\text{C}\)), we can find the total heat transferred, \( q \), using:\[ q = 1258 \,\text{J}/^{\circ}\text{C} \times 13.7^{\circ}\text{C} = 17223.6 \,\text{J} \]
This value represents the total energy change due to the dissolution of calcium chloride. Understanding this heat transfer is crucial for calculating the enthalpy change, which is the focus of the experiment.

Molar mass is a fundamental property of a substance representing the mass of one mole of its molecules. For calcium chloride (\( CaCl_2\)), its molar mass is calculated as:

• 40.08 g/mol for calcium
• 35.45 g/mol for each chlorine ion

The total molar mass of calcium chloride is:\[ 40.08 + 2 \times 35.45 = 110.98 \,\text{g/mol} \]

Having this information allows us to determine how many moles of calcium chloride were dissolved in the experiment. Given 23.6 grams of calcium chloride, the number of moles is:\[ \frac{23.6 \,\text{g}}{110.98 \,\text{g/mol}} \approx 0.2125 \text{ moles} \]Understanding the molar mass is key to calculating the enthalpy change per mole, which tells us how much energy is exchanged when one mole of \( CaCl_2\) dissolves in water.