In constant-pressure calorimetry, how does a calorimeter measure the enthalpy change (ΔH) of a chemical reaction?

• A. By measuring the temperature change of the solution and using the heat capacity to calculate the heat absorbed or released at constant pressure.
• B. By analyzing the color change of the solution to estimate the energy change.
• C. By determining the change in volume of the reactants and products.
• D. By directly measuring the pressure change inside the calorimeter during the reaction.

Answer: (A)

Verified step by step guidance

1. Understand that in constant-pressure calorimetry, the system is maintained at atmospheric pressure, so the heat exchanged corresponds directly to the enthalpy change (\$\Delta H\$) of the reaction.
2. Recognize that the calorimeter contains a solution whose temperature changes as the reaction proceeds, either absorbing or releasing heat.
3. Measure the temperature change (\$\Delta T\$) of the solution during the reaction using a thermometer or temperature sensor.
4. Use the known heat capacity (\$C_p\$) of the solution or calorimeter system to calculate the heat exchanged (\$q_p\$) using the formula: \$\$q_p = C_p \times \Delta T\$\$
5. Since the process occurs at constant pressure, equate the heat exchanged to the enthalpy change: \$\$\Delta H = q_p\$\$ Thus, by measuring the temperature change and knowing the heat capacity, the calorimeter allows determination of \$\Delta H\$.