What statements are true for the Hydrophobic Effect.
1/ The system increases the solvent-exposed area of non-polar parts, which makes more water molecules bound to the hydrophobic regions.
2/ The system makes the solvent-exposed area of non-polar parts smaller, which reduces the number of ordered water molecules. The fled water molecules become free to move, thereby increasing ΔS. As a result, the non-polar region of the molecules clusters together.
3/ The system makes the solvent-exposed area of non-polar parts smaller, which reduces the number of ordered water molecules. The fled water molecules become free to move, thereby increasing ΔH. As a result, the non-polar regions of the molecules clusters together.
4/ Non-polar solutes have a propensity to come together, which is the driving force to exclude water molecules from them.
I personally think, 2 is correct and but 3 and 4 are, I don't understand.
does enthalpy have anything to do with the system reaction and the 4?
The hydrophobic effect is a phenomenon observed when non-polar molecules or groups in a solution tend to aggregate together, while excluding water molecules from their vicinity. Let's evaluate each statement to determine which ones are true:
1/ The statement that "the system increases the solvent-exposed area of non-polar parts, which makes more water molecules bound to the hydrophobic regions" is incorrect. In fact, the hydrophobic effect occurs because non-polar substances do not readily interact with water molecules. Therefore, they tend to minimize their contact with water by clustering together and reducing the solvent-exposed area of their non-polar parts.
2/ The statement that "the system makes the solvent-exposed area of non-polar parts smaller, which reduces the number of ordered water molecules. The fled water molecules become free to move, thereby increasing ΔS. As a result, the non-polar region of the molecules clusters together" is correct. This statement accurately explains the hydrophobic effect. By reducing the surface area of non-polar regions exposed to water, the organized structure of water molecules around the non-polar parts is disrupted, increasing the entropy of the system. This entropy-driven process leads to the clustering of non-polar regions.
3/ The statement that "the system makes the solvent-exposed area of non-polar parts smaller, which reduces the number of ordered water molecules. The fled water molecules become free to move, thereby increasing ΔH. As a result, the non-polar regions of the molecules cluster together" is incorrect. ΔH refers to the change in enthalpy, which is a measure of heat or energy in a system. The hydrophobic effect is primarily an entropy-driven phenomenon, not an enthalpy-driven one.
4/ The statement that "non-polar solutes have a propensity to come together, which is the driving force to exclude water molecules from them" is correct. Non-polar substances naturally tend to aggregate together due to the hydrophobic effect, thereby excluding water molecules from their vicinity.
In summary, the correct statements regarding the hydrophobic effect are 2 and 4. Statement 2 explains the role of entropy in clustering non-polar regions, while statement 4 describes the driving force behind the exclusion of water molecules by non-polar solutes.