Gasoline is primarily a mixture of hydrocarbons and is sold with an octane rating that is based on a comparison with the combustion properties of isooctane. Gasoline usually contains an isomer of isooctane called tetramethylbutane (C8H18), which has an enthalpy of vaporization of 43.3 kJ/mol and a boiling point of 106.5°C. Determine the vapor pressure of tetramethylbutane on a very hot summer day when the temperature is 38°C.

A. 47.9 torr
B. 67.8 torr
C. 89.3 torr
D. 80.3 torr
E. 36.7 torr

Air (consisting mostly of nitrogen (N2), oxygen (O2), and argon (Ar)) dissolves in water due to?

A. dipole-induced dipole forces.
B. ion–dipole forces.
C. dipole–dipole forces.
D. hydrogen bonding.
E. dispersion forces.

Answers:

Option B

Option A.

Explanation:

For part A

The applicable equation is the Clausius-Clapeyron equation. The equation relates the vapor pressure and temperature like this:

We know that P₁ = 6.63 torr

R = 8.314 kj/mol

T₁ = 106.5⁰ = 379.65 K

T₂ = 38⁰ = 311.15 K

ΔH = 43 300J/mol

using the equation to solve for P₂, we get 67.8 torr

For part B

Water is a polar molecule. The bonds in the water are hydrogen bonds; water forms strong hydrogen bonds between the molecules. However, the gases in the air are non polar. Nitrogen and argon are inert gases - nonreactive. Nitrogen has a triple bond N≡N and argon is inert. Oxygen is a bi-atomic gas, O₂.

Hence the only forces in the water with the gases are  dipole-induced dipole forces.

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