Chemistry
Chemistry
Problem
A chemistry student adds a measured mass of solid sodium hydroxide pellets to a coffee-cup calorimeter containing an aqueous solution originally at . The temperature of the solution rises rapidly to before slowly drifting back toward room temperature. Answer the following questions about the thermal changes that occurred. a. Describe the direction of energy transfer between the dissolving solid and the surrounding solution while the temperature was rising. b. Identify the sign (positive or negative) of the enthalpy change per mole for the dissolution of sodium hydroxide and justify your answer in terms of the observed temperature change. c. Explain why the numerical value of the heat released by the dissolving solid is equal in magnitude but opposite in sign to the heat absorbed by the solution in the calorimeter.Intuitive explanation
This problem is about exothermic dissolution and heat transfer — recognizing that dissolving NaOH releases energy into the solution, raising its temperature. The key insight is that the rapid temperature jump tells you how much heat was released by the reaction, which you can calculate using for the solution, then connect back to the moles of NaOH that dissolved. The slow drift back down is just heat loss to the surroundings, not part of the reaction itself.
Intuitive explanation
This problem is about exothermic dissolution and heat transfer — recognizing that dissolving NaOH releases energy into the solution, raising its temperature. The key insight is that the rapid temperature jump tells you how much heat was released by the reaction, which you can calculate using for the solution, then connect back to the moles of NaOH that dissolved. The slow drift back down is just heat loss to the surroundings, not part of the reaction itself.