Question

(A) Predict whether the change in entropy (ΔS) is positive, negative or near zero for the following processes at 298K. Provide a molecular level explanation or justification for your prediction . (B) Now calculate the change in entropy (ΔS) for the following processes at 298K . Write a brief explanation on how your predicted vs. calculated results compare. i. H2O (s) → H2O (l), melting of ice. ii. Formation reaction for steam (water vapor, H2O (g)). iii. C3H8 (l) → C3H8 (aq), Liquid propane going to aqueous propane. iv. The hydrolysis of the dipeptide glycylglycine.

All assumptions need to be clearly and concisely stated. If thermodynamic parameters are used, the citation, reference or link to where this thermodynamics data came from must be stated

Answer 1

Solution:

Entropy is the measurement of randomness or disorder. The change in entropy (ΔS) is positive, when process tends to increase disorder. The entropy of gases are higher than liquids and solids because in gases weak dispersionforces causes increase in disorder while in solids strong intermolecular forces decreases disorder.

I) H2O (s) = H2O (l)

The entropy of liquid is higher than solid, therefore change in entropy is positive.

Thus, ΔS = +ve

II) Formation reaction of water vapor.

H2O(l) = H2O(g)

ΔS = + ve

Entropy of gas is higher than liquids.

III) C3H8 (l) = C3H8(aq)

ΔS = +ve

The entropy of aqueous solution is higher than liquid state due to higher randomness.

IV) Hydrolysis of dipeptide glycylglycine:

ΔS = +ve

Hydrolysis causes an increase in entropy because it leads to increase the disorder. Thus, entropy change of the process is positive.