How can you determine the enthalpy for a reaction in an aqueous solution?

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Question restatement: How can you determine the enthalpy for a reaction in an aqueous solution?

Option 1: Calculate using the specific heat of each of the reactants. This approach is flawed because enthalpy changes in solution are typically determined from the heat absorbed or evolved by the entire system including the solution, not by summing the specific heats of the pure reactants. In aqueous reactions, the relevant heat exchange involves the solution, the calorimeter, and the reaction mixture, not just the reactants individually’s specific heats.

Option 2: Mix the reactants in a calorimeter and measure the temperature change. This is the standard method in calorimetry for aqueous reactions. By measuring the temperature change of the solution and knowing the total mass and the specific heat capacity (often approximated by that of water), you can calculate the heat exchanged (q = m c ΔT) and thus determine the enthalpy change (ΔH) per mole of reaction, assuming constant pressure and complete reaction.

Option 3: Calculate using the mass of the reactants and the solubility constant. The solubility constant describes how much substance dissolves at a given temperature, not the heat released or absorbed during the reaction. It does not directly give the enthalpy change, so this method does not determine ΔH accurately for most reactions in solution.

Option 4: The enthalpy change for this type of reaction cannot be determined. This statement is incorrect for typical aqueous reactions that can be studied calorimetrically. While some reactions may be difficult to analyze, the standard calorimetric approach provides a viable path to ΔH for many aqueous processes.

In summary, the reliable experimental route for determining the enthalpy of an aqueous reaction is to perform calorimetry in a calorimeter and observe the resulting temperature change, then apply q = m c ΔT to relate heat exchange to the enthalpy change. The other options misstate the role of specific heat, misinterpret solubility data, or incorrectly claim impossibility of measurement in this context.

Chemistry (H) - Varnold - Preparatory Academy - 2nd Semester - 2024/2025 2025 Thermochemistry Practice Test

How can you determine the enthalpy for a reaction in an aqueous solution?

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