1. Consider the effect of water concentration on rate of the reaction in water and acetone. WOuld you predict that the rate would be greater or less in the presence of a higher concentration of water? Explain your answer, using the structure of the transition state.
2. Consider the following: You accidentally use 50/50 2-propanol/water instead of 50/50 acetone/water mix. Would you predict that the reaction rate would be higher with acetone/water or with 2-propanol/water? Explain reasoning. (Acetone is a polar aprotic solvent and 2-propanol is a polar protic solvent)
1. To predict the effect of water concentration on the rate of a reaction, we need to consider the nature of the solvent and the transition state of the reaction.
Water is a polar solvent that can stabilize and solvate charged species. Acetone, on the other hand, is also a polar solvent but is less capable of stabilizing charged species due to its lower dielectric constant.
In a reaction, the transition state is a high-energy intermediate that determines the rate of the reaction. The structure and stability of the transition state can be influenced by the polarity of the solvent.
When the concentration of water is high, there are more water molecules present in the solution. These water molecules can interact and solvate the charged or polar intermediates and transition states, stabilizing them and lowering their energy. As a result, the rate of the reaction can increase.
Therefore, we can predict that the rate of the reaction would be greater in the presence of a higher concentration of water.
2. To predict the effect of using a 50/50 2-propanol/water mixture instead of a 50/50 acetone/water mixture on the reaction rate, we need to consider the differences between 2-propanol and acetone as solvents.
Acetone is a polar aprotic solvent, meaning it can dissolve polar compounds without providing or accepting protons (H+ ions). It can stabilize and solvate charged species and polar intermediates effectively.
2-propanol, on the other hand, is a polar protic solvent, meaning it can dissolve polar compounds and can also provide or accept protons. It can form hydrogen bonds with other molecules, including the reactants and intermediates.
Protic solvents like 2-propanol can have a stronger impact on the reaction rate compared to aprotic solvents like acetone. The presence of 2-propanol can lead to increased solvation of reactants and intermediates, enhancing their stability and lowering their energy.
Therefore, we can predict that the reaction rate would be higher with the 2-propanol/water mixture compared to the acetone/water mixture due to the greater solvation effects provided by the polar protic solvent.