A student investigates the thermal effect of dissolving solid sodium hydroxide pellets in water.
• A well-insulated coffee-cup calorimeter contains 100.0 g of water at an initial temperature of 22.0 °C.
• After 3.00 g of NaOH pellets are added and completely dissolve, the final temperature of the solution is 35.6 °C.
Assume the solution has the same density and specific heat capacity as pure water.
Answer the following in the spaces provided.
(a) Clearly identify the system and the surroundings for this experiment.
(b) Describe the direction of heat flow during the process and classify the dissolution of NaOH as exothermic or endothermic. Justify your classification using the temperature data.
(c) The student plans to calculate the molar enthalpy change for the dissolution process by dividing the heat exchanged, q, by the number of moles of NaOH that dissolved. Explain why the resulting value for ΔH should be reported with a negative sign, even though the student will obtain a positive value for q when substituting the temperature change into q=mcΔT. In your explanation, refer explicitly to the definitions of q and ΔH for the system.