Earlier I asked does the following represent an equilibrium situation:

1) A glass of iced tea still has sugar at the bottom after several minutes of stirring.

If no more sugar can be dissolved could you explain why that represents an equilibrium? Please

Yes. We have water (or close to it) with a solution of sugar with some sugar as the solid and no more can dissolve. Some sugar is dissolving and for every molecule of sugar that dissolves another one that is in solution crystallizes. That is what dynamic equilibrium is all about. Some molecules change phase (going into solution) while others change phase (crystallizing from solution). The amount of sugar is solution; however, STAYS THE SAME.

To determine if the situation represents an equilibrium, we need to understand the concept of equilibrium in a solution.

Equilibrium in a solution occurs when the rate of dissolution of a solute (in this case, sugar) into a solvent (water in the iced tea) is equal to the rate of precipitation (crystallization) of the solute. In other words, the dissolved particles are being removed from the solution and being added back at the same rate.

In the given scenario, after stirring the glass of iced tea for several minutes, if no more sugar can be dissolved, it suggests that the solution has reached its saturation point. At this point, the rate of sugar dissolving into the tea and the rate of sugar precipitating from the solution are in balance, resulting in no net change in the overall concentration of sugar in the tea.

When an equilibrium is reached, it means that the forward and backward processes are occurring at the same rate. In this case, the forward process is the dissolution of sugar into the tea, and the backward process is the precipitation of sugar as it reaches its solubility limit. Since no more sugar can be dissolved, it implies that the solution is at equilibrium because the rate of dissolution is equal to the rate of precipitation.

Therefore, the presence of undissolved sugar at the bottom of the glass of iced tea after several minutes of stirring represents an equilibrium situation.