Question

What is the effect of temperature of solubility of $KN{O_3}$ and $CaS{O_4}$ in water?

Answer 1

We must remember that solute solubility is dependent on temperature. When solid is soluble in a liquid, there is a change in the physical state of the solid similar to melting. Heat is necessary to break the bonds that hold the molecules in the solid together. At the same time, heat is released off during the formation of new solute - solvent bonds.

Complete step by step answer:

Endothermic reaction: Those reactions that absorb heat energy from the surroundings are called endothermic reactions. The breakage of chemical bonds absorbs heat energy.
Example: In the process of photosynthesis, carbon dioxide and water are converted to free oxygen and glucose by absorbing heat energy.
${\text{6}}\,{\text{C}}{{\text{O}}_{\text{2}}}{\text{ + 6}}\,{{\text{H}}_{\text{2}}}{\text{O + 2519}}\,{\text{kJ}}\xrightarrow{{}}{{\text{C}}_{\text{6}}}{{\text{H}}_{{\text{12}}}}{{\text{O}}_{\text{6}}}{\text{ + 6}}{{\text{O}}_{\text{2}}}$
Exothermic reaction: Those reactions that release heat energy to the surroundings are called exothermic reactions. The formation of chemical bonds, releases heat energy.
Example: In the combination reaction of solid carbon and gaseous oxygen, formation of gaseous carbon dioxide takes place with the evolution of heat energy.
${\text{C}}\left( {\text{s}} \right){\text{ + }}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right)\xrightarrow{{}}{\text{C}}{{\text{O}}_{\text{2}}}\left( {\text{g}} \right){\text{ + 393}}\,{\text{kJ}}$
We have to know that in the endothermic reaction more of the solid is dissociated while in the exothermic reaction less of the solid is dissociated.
If the solubility of compounds increases with increase in temperature, then the process of dissolution is an endothermic process.
If the solubility of compounds decreases with increase in temperature, then the process of dissolution is an exothermic process.
With an increase in temperature, the solubility of potassium nitrate $\left( {{\text{KN}}{{\text{O}}_{\text{3}}}} \right)$ increases in water.
With a decrease in temperature, the solubility of calcium sulfate $\left( {{\text{CaS}}{{\text{O}}_{\text{4}}}} \right)$ decreases in water.
Dissolution of potassium nitrate in water is an endothermic process and dissolution of calcium sulfate in water is an exothermic process.

Note:
For several solids dissolved in liquid water, the solubility raises with temperature. The increase in kinetic energy which comes with higher temperatures permits the molecules of solvent to more effectively break apart the solute molecules which are held together by intermolecular attractions. The increase in vibration (kinetic energy) of the solute molecules makes them more readily soluble since they are less able to hold together.