Suppose you were investigating the correlation between intermolecular forces and the way in which molecules cohere to each other in a liquid and decided that you can gain some insight by comparing the entropies of vaporization of several liquids.

Calculate the entropy of vaporization of acetone at 296 K with an external pressure of 1 bar. The molar heat capacity of liquid acetone is 127 J · K^–1 · mol^–1, its boiling point is 329.4 K, and its enthalpy of vaporization is 29.1 kJ · mol^–1.

PLAN

Step 1 Use Eq. 4 to calculate the entropy change accompanying the heating of acetone from the “initial” temperature of 296 K to the “final” temperature of 329.4 K. The heat capacity of liquid acetone is approximately constant over this range.

Step 2 Use Eq. 5 to calculate the entropy of vaporization or look up the value in Table 4F.1.

Step 3 Use Eq. 4 to calculate the entropy change accompanying the cooling of acetone vapor from the new “initial” temperature of 329.4 K back to the new “final” temperature of 296 K (a negative value). The heat capacity of acetone vapor may be estimated from the equipartition theorem (Topic 4B) as C_P,m = 4R.

Step 4 Sum the three entropy changes to give DS_vap°(296 K).

What should you assume? Assume that acetone vapor is an ideal gas and that only translations and rotations contribute to the gas-phase heat capacity.

Transcribed Image Text:

T₂ Cln Ti AS C ln- =