Question

It is found when an unknown solid solute is dissolved in water that the solubility of the solid decreases if temperature is increased. In the dissolution of this unknown solid Is entropy increased or decreasec and is it endothermic or exothermic. and why?

Answer 1

As stated in above question solubility decreases with increased temperature. The reaction with increased entropy is always favored and solid dissolving in water always increases entropy. But as we can see here increase in temperature is causing the unknown solid to be less soluble. This means that increase in temperature is causing some disturbances in intermolecular forces and it is difficult for solute to dissolve. These means entropy decreases at increased temperature.

In case of dissolving solute, if the process is endothermic, the system will use all the heat given and use it to its favor and dissolve solute completely and solubility will increase with increasing temperature. But in our case increased heat is causing less solubility. Meaning heat cannot leave the system. We can easily deduce that dissolution is exothermic.