The correct option is Highly exothermic process.
Explanation
The process of mixing concentrated acids or bases with water is known as dilution. From a thermodynamic perspective, this involves the interaction between solute ions and solvent molecules, resulting in a net energy change.
Detailed Analysis:
- Hydration of Ions: When a concentrated acid or base is added to water, it dissociates into ions (e.g., \(H^+\) or \(OH^-\)). These ions interact strongly with polar water molecules, a process known as hydration.
- Exothermic Nature: The hydration process releases a significant amount of energy (hydration energy). This energy release is much higher than the energy consumed to break the bonds in the acid or base. Consequently, the overall enthalpy change (\(\Delta H\)) is negative, making the reaction highly exothermic.
- Safety Consequence: The heat generated can be intense enough to cause the solution to boil instantly or splash. This is why the standard safety rule dictates adding acid to water slowly with constant stirring, allowing the generated heat to dissipate into the larger volume of water. Adding water to concentrated acid can cause dangerous splashing due to rapid vaporization.
Key Takeaway:
The dilution of concentrated acids and bases is a highly exothermic process due to the release of large amounts of hydration energy.