11. Determining the molecufar contributions to the hydrophobic effect-Enthalpic

Question

11. Determining the molecufar contributions to the hydrophobic effect-Enthalpic effects: al In general, does a nonpolar molecule have stronger interactions with another nanpolar moletule, or with a water molecule? A nonpolar molecule would experience a stronger cling to: D another nonpolar solute D a water molecule b) As nonpolar molecules cluster together in an aqueous solution, would the change in how the nonpolar solute interacts with its new neighbors contribute an Dincrease (+AH) or a D decrease (-AH) in enthalpy? ) Which has stronger intermolecular interactions, D a water molecule interacting with a nonpolar solute, or D a water molecule interacting with a water molecule? d) Water interacting only with other waters form about four hydrogen bonds with its neighbors. Researchers were somewhat surprised to find that, at 25" C, a water molecule at the nonpolar interface interfacial water) forms the same average number of hydrogen bonds (4) to other waters! Even in the presence of gt the nonpolar solute, water can find enough nearby water to hydrogen bond with. Given hydrogen bonding is the main interaction each water participates in, do you expect the enthalpy o water to change as nonpolar molecules cluster together in an aqueous solution? Yes No e) Enthalpy conclusion: When nonpolar solutes coalesce in water, it is expected that the overall enthalpy would increase significantly, decrease significantly, stay about the same(select all possibiities based on your answers abovel. f) Reality check: is your conclusion consistent with the data in Table 2-2 above? Explain Yes No 8l The hydrophobic effect is caused by the system minimizing the number of waters at a nonpolar interface, as these interfacial waters have restricted motion. Is this conclusion supported by the data in Table 2.2? Give the evidence you use to draw your conclusion. h) The term hydrophobic effect a bit of a misnomer. Based on your conclusion, why is that?

Explanation / Answer

1a) In non polar molecules the force of attraction are weak Vander Waal forces . Water is a polar molecule and have dipole. This means there is no common type of force of attraction between a non polar and a polar water molecules.

So, a non polar molecule will experience a stronger cling to

Another non polar solute.

b) As it is clear from a) that a non polar solute will not interact with polar/aqueous solvent. So, energy will be required(supplied) to make a solution of non polar solute in polar solvent. So,

H increase

c) As explained above

A water molecule interacting with a water molecule will have stronger intermolecular interaction.

d) As per statement , the hydrogen bonding is the main interaction each water molecule participate in, and non polar molecule donot involve in hydrogen bonding with polar water molecules. So, there will be no interaction between these two and hence there will be no enthalpy change in water. So, the answer is NO.

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