Highest Vapor Pressure Prediction

Which of the following would you predict to have the highest vapor pressure?

A. ethyl methyl ketone

B. n-ethyl propenamide

C. diethyl ether

D. cyclopentane

E. ethyl methyl ketone

Final answer:

Answer:

Diethyl ether has the highest vapor pressure among the given compounds due to its weaker intermolecular forces.

Vapor pressure is defined as the measure of the tendency of a material to change into the gaseous state or to the vapor state. Vapor pressure increases with the temperature. The higher the vapor pressure of a substance signifies the greater the concentration of the compound in the gaseous phase of the material and the greater the extent of vaporization of the material.

Vapor pressure is said to be dependent upon the temperature. It is determined that a greater number of vapor molecules that strikes the container walls more frequently results in an increase in the vapor pressure. Vapor pressure is called as the pressure which caused by the evaporation of liquids.

Three common factors that influence vapor pressure are surface area, intermolecular forces, and temperature. Diethyl ether has a very small dipole and most of its intermolecular attractions are London forces. Although this molecule is the largest of the four under consideration, its IMFs are the weakest and, as a result, its molecules most readily escape from the liquid. It also has the highest vapor pressure.

Due to its smaller size, ethanol exhibits weaker dispersion forces than diethyl ether. However, ethanol is capable of hydrogen bonding and, therefore, exhibits stronger overall IMFs, which means that fewer molecules escape from the liquid at any given temperature, and so ethanol has a lower vapor pressure than diethyl ether.

Water is much smaller than either of the previous substances and exhibits weaker dispersion forces, but its extensive hydrogen bonding provides stronger intermolecular attractions, fewer molecules escaping the liquid, and a lower vapor pressure than for either diethyl ether or ethanol.

Ethylene glycol has two -OH groups, so, like water, it exhibits extensive hydrogen bonding. It is much larger than water and thus experiences larger London forces. Its overall IMFs are the largest of these four substances, which means its vaporization rate will be the slowest and, consequently, its vapor pressure the lowest.