Please tell me how can rate …

When a solid solute is added  to the solvent like water , some solute dissolves  and its concentration increases in solution . This proces is known as as ' dissolution ' . Some solute particles in solution  collide with solid solute particles and get separated out of solution . This process is known as ' crystallisation '. A stage is reached when the ttwo processes occur at the same rate and thus a dynamic equilibrium is reached ,

..............................................Dissolution <----------->  crystallisation

Factors affecting the rate of dissolution :

(i)  Effect  of temperature -  

The  rate of dissolution of a solid in a liquid is significantly affected  by temperature changes  as  the above dynamic equilibria must follow LeChatelier's Principle. In general , if the dissolution process is endothermic  ( {tex}\Delta H{/tex} _sol < 0 ) , the solubility increases with rise in temperature. and if it is exothermic ( {tex}\Delta H{/tex} _sol > 0 )   the rate of dissolution   decreases . These trends have been experimentally observed governing the concerned rate law too..

(ii) Effect of pressure -

Since both solids as well as liquids are highly incompressible , variations of pressure does not have any significant effect on tthe process or rate of dissolution of a solid in water.