Use the observation in the first column to answer the question in the second col

Question

Use the observation in the first column to answer the question in the second column. Observation At 25 degree C, Substance C has a vapor pressure of 136. torr and Substance D has a vapor pressure of 186. Question Which has a higher enthalpy of vaporization? Substance C Substance D Neither, C and D have the same enthalpy of vaporization. It's impossible to know without more information. At 1 atm pressure. Substance A boils at 109. degree C and Substance B boils at 125. degree C. Which has a higher vapor pressure? Substance A Substance B Neither, A and B have the same vapor pressure. It's impossible to know without more information. The enthalpy of vaporization of Substance E is smaller than that of Substance F. At any temperature where both substances are liquid, which has the higher vapor pressure? Substance E Substance F Neither, E and F have the same vapor pressure. It's impossible to know without more information.

Explanation / Answer

1. Substance C

Vapor pressure (VP) of C = 136 torr and VP of D = 186 torr. Since VP (C) < VP (D), one needs to supply more energy to get C into the vapor phase. Hence enthalpy of vaporization of C will be higher.

2. Substance A

B.pt (A) = 109 C

B,pt (B) = 125 C

Since A boils at a lower temperature than B, A will have a higher vapor pressure.

3. Substance E

Since E has a lower enthalpy of vaporization, it can be brought into the vapor phase with lower energy as compared to F. Hence, E will have a higher vapor pressure.

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