Final answer:
The dissolution of borax in water can have both a positive (endothermic) or negative (exothermic) change in enthalpy. The spontaneity of any process is determined by the Gibbs free energy (ΔG), which must be negative for the process to be spontaneous, while the change in enthalpy (ΔH) can be either positive or negative, depending on temperature and entropy (ΔS) changes.
Step-by-step explanation:
If the dissolution of borax in water is spontaneous, the change in enthalpy can be either positive or negative, which corresponds to both endothermic and exothermic processes. The spontaneity of a reaction is determined by the Gibbs free energy (ΔG) and not solely by the enthalpy change (ΔH). For a process to be spontaneous, ΔG must be negative. However, depending on the temperature and the change in entropy (ΔS), a spontaneous process can have either a positive or negative ΔH.
Key Points to Consider
- Spontaneous processes have a negative ΔG.
- A positive ΔH indicates an endothermic process, whereas a negative ΔH indicates an exothermic process.
- The sign of ΔH for a spontaneous process can be both positive and negative depending on ΔS and the temperature.
In the given example about the dissolution of KCl, since the process is endothermic (the temperature decreases), the ΔH is positive; however, the overall process of borax dissolution could be endothermic or exothermic and still be spontaneous. The spontaneity is ultimately driven by a positive ΔS and the temperature conditions.