Answer to Question #155517 in General Chemistry for Anonymous

Question

The heat needed to vaporize a certain amount of liquid. A certain substance A has a boiling point of 78 degrees celcius and substance B has boiling point of 100 degrees celcius

Answer 1

A ‒ boiling point TB = 78 ⁰C

B ‒ boiling point TB = 100 ⁰C

Liquids are called condensed phases because their particles are packed in close proximity to one another. The intermolecular forces (IMFs) between the molecules that make up liquids vary in strength, and this variation results in a broad range of physical properties among liquids.

As the strength of the IMFs in a series of liquids increases, the boiling points of the liquids increase. Substance B with higher boiling point (TB = 100 ⁰C) has a stronger IMFs (force of attraction).

The strength of the IMFs in the liquid is a direct indication of the enthalpy of vaporization (heat of vaporization). The IMFs in substance B (TB = 100 ⁰C) are stronger, so the enthalpy of vaporization is greater than that of substance A.

As the strength of the IMFs in a series of liquids increases, the vapor pressures of the liquids decrease. That’s why substance A (TB = 78 ⁰C) has a higher heat of vaporization than that of substance B.

Strong IMFs result in high viscosity for a liquid. Substance B (TB = 100 ⁰C) will have a higher viscosity.