Given that ΔGrxn>0, how do you explain that some of the borax actually dissolves at 25deg C?
To explain why some of the borax actually dissolves at 25°C even when ΔGrxn is greater than 0, there are a few factors to consider.
First, it's important to understand that the sign of ΔGrxn (Gibbs Free Energy change) indicates the direction of the spontaneous reaction. When ΔGrxn is positive (greater than 0), it means that the reaction is non-spontaneous in the forward direction and thermodynamically unfavorable.
However, the solubility of a compound also depends on factors such as the concentration of the solute, temperature, and pressure. In this case, we need to focus on the temperature.
Although the reaction may not be spontaneous in the forward direction (dissolving), there can still be an equilibrium established between the dissolved and undissolved borax. This equilibrium is influenced by factors such as temperature and concentration.
At 25°C, although ΔGrxn is positive, the solubility of borax might still be sufficient to allow a fraction of it to dissolve. This could be due to the kinetic energy of the borax molecules, which increases with temperature. The increased kinetic energy can enhance the chances of individual borax molecules breaking apart from the crystal lattice and entering into the solution.
Moreover, the dissolution of some borax at 25°C does not mean the reaction is spontaneous in the forward direction. It simply means that a dynamic equilibrium is established, where the rate of dissolution is balanced by the rate of precipitation or re-crystallization. At this temperature, the rate of dissolution and re-crystallization reaches an equilibrium point, resulting in a non-zero concentration of dissolved borax.
So, even though the overall reaction of borax dissolving at 25°C is thermodynamically unfavorable (ΔGrxn>0), the kinetic factors and the establishment of dynamic equilibrium allow for some of the borax to dissolve.