Final answer:
Adding NaOH swiftly to the reaction mixture is crucial to ensure the reaction occurs promptly after mixing and that the calorimeter measures only the temperature change due to the reaction, verifying Hess's law accurately.
Step-by-step explanation:
To ensure accuracy when measuring reaction enthalpies (∆h) and to verify Hess's law, it is critical to add NaOH quickly to the reaction mixture.
Doing this minimizes energy loss and helps maintain consistent conditions within the calorimeter. Swift addition allows us to assume that the reaction between NaOH and HCl occurs instantly after mixing, ensuring that the temperature change measured by the thermometer is solely due to the reaction taking place, and not the process of mixing.
Since enthalpy is a state function, the path taken to reach the final state does not affect the enthalpy change. Under controlled conditions, we can use calorimetry data to calculate the ∆H of the overall reaction.
According to Hess's law, we can also sum the enthalpy changes from individual steps of a reaction, giving us an indirect method to determine enthalpies for reactions that are challenging to measure directly.