Assuming the dissolution of borax in water is a spontaneous reaction, do you expect the change in enthalpy to be positive or negative or are both signs possible? Explain your answer
A. Neither, enthalpy does not change, the positive entropy for the dissolution, leads to –G(G=H–TS;G=–T(+S).
B. Positive, the absorption of energy creates a spontaneous reaction.
C. Negative, the process of ionization releases energy into solution allowing for a spontaneous reaction.
D. Both, the reaction is spontaneous at high temperatures if H is positive and always spontaneous if H is negative.
E. More information is required.
I would be interested in your thinking on this. And why?
To determine whether the change in enthalpy (ΔH) for the dissolution of borax in water is positive or negative, we need to consider the spontaneity of the reaction and the relationship between enthalpy, entropy, and Gibbs free energy. The answer lies in understanding how these variables are interconnected.
Spontaneous reactions are those that occur without external intervention and tend to proceed in the direction that favors the formation of products. In the context of dissolution, if borax dissolves spontaneously in water, it means that the dissolved ions are more stable and favored over the solid form.
Based on the options provided:
A. The statement suggests that neither positive nor negative ΔH is expected and that enthalpy does not change. It indicates that the positive entropy (ΔS) associated with the dissolution makes the free energy change (ΔG) negative, leading to spontaneous dissolving. However, this explanation overlooks the fact that ΔH is related to the enthalpy change, which is directly connected to the heat absorbed or released during the dissolving process. Hence, option A can be ruled out.
B. This option suggests that the absorption of energy creates a spontaneous reaction. It implies that the dissolution process requires energy and therefore has a positive ΔH. However, this contradicts the principle that spontaneous reactions tend to proceed towards lower energy states. So, option B can also be ruled out.
C. This option suggests that the process of ionization releases energy into the solution, leading to a spontaneous reaction. By releasing energy, the ΔH would be negative. This aligns with the principle that spontaneous reactions are often associated with more stable, lower-energy states. Hence, option C is a plausible explanation for the spontaneous dissolution of borax.
D. This option suggests that both positive and negative ΔH are possible, depending on the temperature. It states that the reaction is spontaneous at high temperatures if ΔH is positive. However, this contradicts the fact that spontaneous reactions tend to have negative ΔH at all temperatures. Therefore, option D can also be ruled out.
E. The final option states that more information is required to determine the answer. While it is always beneficial to have more information for a comprehensive analysis, in this case, the information provided can lead us to a definite answer.
Based on the reasoning above, option C is the most appropriate answer. The process of ionization releases energy into the solution, resulting in a negative change in enthalpy, which aligns with the spontaneous dissolution of borax in water.