how does stirring affect the rate at which a solute dissolves in a solvent?
This really should be pretty obvious. If you place a solute in a solvent, the region of the solvent around the solute will have a higher concentration of the solute than elsewhere in solution. There is almost always a tendency to re-deposit crystals of the solute. Stirring the mixture disperses the dissolved material and lowers the concentration of dissolved solute next to the undissolved solute. Thus, there is an increased tendency for the solute to dissolve. Think of putting salt in water. You can actually see the salt dissolving. If you stir, the water distributes the dissolved salt away from the salt crystals. Thus, there is less tendency to redeposit salt crystals and greater tendency to dissolve the existing salt crystals. Thus, it speeds up the dissolution of the salt.
