Question

Consider the following two substances and their vapor pressures at 298 K.

Substance Vapor pressure (mmHg)
A 275
B 459
Based on this information, compare the characteristics of the two substances.
1. Substance A or substance B:
a. Has weaker intermolecular forces?
b. Has a higher boiling point?
c. is a gas at 300mmHg?
d. has a higher heat of vaporization?

Answer 1

Comparing the two substances, A and B

a) B has weaker in intermolecular forces.

b) A has a higher boiling point.

c) B is a gas at 300mmHg.

d) A has a higher heat of vaporization

The reason for this is because vapour pressure is the measure of the pressure exerted by a gas above a liquid in a closed container. Strong intermolecular forces produce a lower rate of evaporation and a lower vapor pressure. Weak intermolecular forces produce a higher rate of evaporation and a higher vapor pressure.

Answer 2

Based on the information, the comparison of characteristics of two substances is as follow:

Substance A:

• Has a higher boiling point
• Has a higher heat of vaporization

Substance B:

• Has weaker intermolecular forces
• Is a gas at 300 mmHg

Step-by-step explanation:

• The substance A has vapor pressure 275 mmHg so it has low vapor as compared to substance B so it has higher boiling point and has higher heat of vaporization.
• The substance B has vapor pressure of 459 mmHg so it has weaker intermolecular forces as compared to substance A and also it is a gas at 300 mmHg.