Reading Quiz

Question 1:

Answer:

1. It decreases by kT/N_A for every molecule of B added.
2. The chemical potential of A should decrease. This is stated on the next page and from equation 5.59 we see increasing NB will decrease uA.
3. The chemical potential of solvent A decreases as more solute B is added.
4. As more solute is added, the chemical potential of the solvent decreases.
5. It gets smaller.
6. The chemical potential of solvent A, given in 5.69, will go down as more solute B is added because of the N_b term on top of the second term in the equation.
7. As more solute is added, N_B gets bigger, so you're subtracting a larger number from mu_0, and the chemical potential of the solvent gets smaller.
8. As N_B increases, mu_A decreases.
9. The chemical potential of solvent A reduces as more solute B is added.
10. It decreases

Question 2:

Answer:

1. A semi-permeable membrane allows passage of solvent but not solute. An example is dialysis tubing. Osmosis is the spontaneous flow of solute across such a membrane.
2. A semi-permeable membrane lets some things pass through (solvent) and not others (solute).8ju -0poooll Osmosis is the flow of pure solvent particles into a solution through the membrane.
3. A semi-permeable membrane is a membrane that only allows solvent molecules to pass through it: solvent molecules cannot pass. Osmosis is the spontaneous flow of solvent molecules from the pure solvent into the solution, or particles flowing toward lower chemical potential.
4. A semi-permeable membrane is a barrier that blocks some substances but allows others to pass through. Osmosis is the flow of a solvent from the pure-solvent side of a semi-permeable barrier to the side with a dilute solution in order to decrease its chemical potential.
5. A semi-permeable membrane is a barrier that allows solvent molecules, but not solute molecules, to pass. Osmosis is the process of solvent molecules spontaneously flowing from a region of pure solvent into a region of solution.
6. A semipermeable membrane is a membrane that only allows the solvent molecules through. Osmosis is the flow of solvent molecules across a semipermeable membrane.
7. A semi-permeable membrane allows solvent molecules to pass through, but not solute molecules, for example, a membrane that allows water from a salt water solution to pass through, but not the salt molecules. Osmosis is the spontaneous flow of solvent molecules from the pure solvent into the solution, when they are separated by such a semi-permeable membrane.
8. semi-permable membrane - a membrane that allows only solvent molecules and not solute molecules to pass through osmosis - the spontaneous flow of solvent molecules from pure solvent into solution
9. A semi-permeable membrane is one that allows only solvent molecules, not solute molecules to pass through. Osmosis is the flow of molecules through a semi-permeable membrane.
10. osmosis is the spontaneous flow of molecules that brings the chemical potentials of a system to the save value. a semi-permeable membrane is a barrier that leaves only solvent molecules through.

Question 3:

Answer:

1. The driving force for osmosis is movement from high solvent chemical potential toward low solvent chemical potential (higher concentration of solute). Pure solvent molecules are not burdened with solvation of solute, so they hit the membrane more often than those of low chemical potential which are busy hosting solute. Thus, the net flow is toward the side with more solute.
2. Since systems try to minimize chemical potential, and the solution has a lower potential, particles will flow from the solvent to the solution. Molecularly there are more 'pure' particles in the pure solvent than the solution so the particles on the solvent will hit more often and more will pass through the membrane.
3. Osmosis at the chemical potential level means that particles want to flow toward the lower chemical potential. At the molecular level, the solvent molecules flow from the pure solvent into the solution.
4. In terms of chemical potentials, the chemical potential of the solvent in the solution is lower than the chemical potential of the pure solvent. The solvent tends to decrease its chemical potential, so it flows towards the solution side. On the molecular level, about the same number of particles hit the barrier on both sides. However, on the pure solvent side, all of these molecules are solvent and pass through. On the solution side, some of the molecules are solute, so fewer solvent molecules pass through the barrier in that direction.
5. The chemical potintial of the solvent in the solution is less then the chemical potential of the pure solvent, and particles tend to flow towards the lower chemical potential. At the molecular level, solvent molecules are hitting the membrane from both sides, yet because of the presence of the solute molecules, there are less particles hitting the membrane from the side of the solution. So the side with the pure solvent exerts more pressure, and solvent molecules flow towards the solution side.
6. Osmosis occurs towards an area of lower chemical potential. The lower potential occurs as more solutes are added to solvents, lowering the chemical potential. This in turn makes the solvent particle across the membrane flow towards this. On a molecular level, more solvent particles are hitting the membrane on the pure solvent side, so more of those particles are able to pass throuhg.
7. As a result of the conclusion in question one above, we expect the chemical potential of the solvent to be lower in the solution than it is in the pure solvent, and thus the solvent will spontaneously flow toward less chemical potential, which is into the solution. On the molecular level, you can think of the molecules actually passing through the membrane. The solution contains solute molecules and thus less of the molecules hitting the membrane in a given time are solvent molecules compared to the pure solvent side, so more solvent molecules will end up passing from the pure solvent into the solution than the other way around.
8. In terms of chemical potential, the second law says that molecules tend to flow toward lower chemical potential. A pure solvent has a higher mu than mu of a solution. From a molecular level, the pressure of the pure solvent is greater than the solution because there are more particles to interact, so there is a net flow toward the solution.
9. When the chemical potentials are equal, no osmosis takes place. When they are not, osmosis causes flow from the greater chemical potential to the lesser chemical potential. The opposite is the case for the number of molecules.
10. Osmosis is alot like heat flow. Heat flow works to equilibrate temperature and osmosis works to equilibrate chemical potentials.

Question 4:

Answer:

1. The reduction occurs because when solvent contains some solute molecules, there are statistically fewer solvent molecules at the gas/liquid interface and evaporation occurs more slowly.
2. The addidtion of solute particles causes the solvent to escape into the vapor less frequently because the solute is simply in the way.
3. The reduction in vapor pressure of a solution occurs because the addition of solute molecules reduces the number of solvent molecules at the surface of the liquid, so they escape into the vapor less frequently.
4. Only molecules at the surface of the liquid escape as vapor. In the solution, fewer solvent molecules are on the surface (since some of the solute has to be there, too), so fewer molecules can escape as vapor.
5. "...the reduction in vapor pressure happens because the addition of solute reduces the number of solvent molecules at the surface of the liquid-- hence they escape into the vapor less frequently" (pg 207)
6. The reduction in vapor pressure occurs because increasing the amount of solute molecules causes less solvent molecules to appear at the open part of the container. This means that less molecules are able to evaporate into vapor. Since pressure is related to the amount of molecules evaporating, less molecules means less pressure.
7. You can think of it this way: in the presence of solute molecules that do not evaporate, the solvent molecules have a harder time getting to the surface of the liquid where they can then hop up into the gas, so there's less evaporation. In order to increase the evaporation rate, you have to decrease the pressure so the molecules can escape easier.
8. The reductions of vapor pressure happens because the addition of solute reduces the number of solvent molecules at the surface of the liquid, so they evaporate less frequency.
9. At the molecular level, the reduction in vapor pressure happens because the addition of solute reduces the number of solvent molecules at the surface of the liquid. They escape into vapor less frequently.
10. This happens because the increase in soute reduces the amount of solvent molecules at the surface of the solution. Thus making them evaporate much slower.

Question 5:

Answer:

1. Does Raoult's law as discussed above only apply to ideal solutions in which there would be no solute/solvent interactions, or does it work for real solutions too?
3. In making eq. 5.90 from eq. 5.89, the author makes T approximately equal T_o on the right-hand side, while the two are still separate entities on the left-hand side. How is this mathematically possible?
6. None.
7. I think I understand the main ideas of this section on dilute solutions, but to be honest I wasn't following all of the equation manipulations going on...
9. I was a bit confused by the derivation for chemical potentials on page 203.
10. -