Intermolecular Forces: Liquids, Solids, and Phase Changes

Butane is a common fuel used in cigarette lighters and camping stoves. Normally supplied in metal containers under pressure, the fuel exists as a mixture of liquid and gas, so high temperatures may cause the container to explode. At ,$\mathbf{25}\mathbf{.}{\mathbf{0}}^o\mathbf{C}$ the vapour pressure of butane is 2.3 atm. What is the pressure in the container at $\mathbf{135}\mathbf{.}{\mathbf{0}}^o\mathbf{C}$ vap ( =24.3 kJ/mol)?                

What is the energy gap in band theory? Compare its size in superconductors, conductors, semiconductors, and insulators.

How does the energy of attraction between particles compare with their energy of motion in a gas and in a solid? As part of your answer, identify two macroscopic properties that differ between a gas and a solid.

(a) Why are gases more easily compressed than liquids?

(b) Why do liquids have a greater ability to flow than solids?

Liquid propane, a widely used fuel, is produced by compressing gaseous propane. During the process, approximately 15 kJ of energy is released for each mole of gas liquefied. Where does this energy come from?

Many heat-sensitive and oxygen-sensitive solids, such as camphor, are purified by warming under a vacuum. The solid vaporizes directly, and the vapour crystallizes on a cool surface. What phase changes are involved in this method?

Liquid hexane (bp:) is placed in a closed container at room temperature. At first, the pressure of the vapour phase increases, but after a short time, it stops changing. Why?

Match each numbered point in the phase diagram for compound Q with the correct molecular depiction below:

The phase diagram for substance A has a solid-liquid line with a positive slope, and that for substance B has a solid-liquid line with a negative slope. What macroscopic property can distinguish A from B? 

Why does water vapour at ${\mathbf{100}}^o\mathbf{C}$ cause a more severe burn than liquid water at  ${\mathbf{100}}^o\mathbf{C}$?

Describe the changes (if any) in potential energy and in kinetic energy among the molecules when gaseous ${\mathbf{PCl}}_{\mathbf{3}}$ condenses to a liquid at a fixed temperature.

A liquid is in equilibrium with its vapour in a closed vessel at a fixed temperature. The vessel is connected by a stopcock to an evacuated vessel. When the stopcock is opened, will the final pressure of the vapour be different from the initial value if

(a) Some liquid remains

(b) All the liquid is first removed?

When benzene is at its melting point, two processes occur simultaneously and balance each other. Describe these processes on the macroscopic and molecular levels.

From the data below, calculate the total heat (in J) needed to convert 22.00 g of ice at -6.00${}^o\mathbf{C}$ to liquid water at 0.500 ${}^o\mathbf{C}$: M.P at 1 atm: 0.0 ${}^o\mathbf{C}$; ${\mathbf{\Delta H}}_{\mathrm{fus}}$ : 6.02 kJ/mol; ${\mathbf{Cl}}_{\mathrm{iquid}}$ : 4.21 J/g${}^o\mathbf{C}$; ${\mathbf{C}}_{\mathrm{solid}}$: 2.09 J/g${}^o\mathbf{C}$ 

From the data below, calculate the total heat (in J) needed to convert 0.333 mole of gaseous ethanol at ${300}^o\mathbf{C}$   and 1 atm to liquid ethanol at $25{.0}^{\mathrm{o}}\mathrm{C}$ and 1 atm: B.P. at 1 atm: , $78{.5}^o\mathbf{C}$;${\mathbf{\Delta H}}_{\mathrm{yap}}$: 40.5 kJ/mol; : ${\mathbf{C}}_{\mathrm{gas}}$1.43 J/ ${\mathbf{g}}^o\mathbf{C}$; : 2.45 J/${\mathbf{g}}^o\mathbf{C}$.

Use these data to draw a qualitative phase diagram for ethylene (${\mathbf{C}}_2{\mathbf{H}}_4$ ). Is  ${\mathbf{C}}_2{\mathbf{H}}_4$ (s) more or less dense than ${\mathbf{C}}_2{\mathbf{H}}_4$ (l)?

bp at 1 atm:  $\mathbf{-}\mathbf{103}\mathbf{.}{\mathbf{7}}^o\mathbf{C}$                          

mp at 1 atm:     $\mathbf{-}\mathbf{169}\mathbf{.}{\mathbf{16}}^o\mathbf{C}$         

Critical point:       $\mathbf{9}\mathbf{.}{\mathbf{9}}^o\mathbf{C}$      and  50.5 atm 

Triple point:           $\mathbf{-}\mathbf{169}\mathbf{.}{\mathbf{17}}^o\mathbf{Cand}\mathbf{1}\mathbf{.}\mathbf{20}\mathbf{\times }{\mathbf{10}}^{-3}\mathbf{atm}$   

Use these data to draw a qualitative phase diagram for . Does  sublime at 0.05atm? Explain. 

MP at 1atm:              13.96 K 

BP at 1atm:              20.39 K                      

Triple point:             13.95 K and 0.07atm 

Critical point:           33.2 K and 13.0atm 

Vapour pressure of solid at 10 K: 0.001atm

A liquid has a ${{\mathbf{\Delta H}}^o}_{\mathrm{vap}}$ of 35.5 kJ/mole and a boiling point of  $\mathbf{122}\mathbf{°}\mathbf{C}$ at 1.00 atm. What is its vapour pressure at $\mathbf{113}\mathbf{°}\mathbf{C}$ ?

Diethyl ether has a ${{\mathbf{\Delta H}}^o}_{\mathrm{vap}}$ of 29.1 kJ/mole and a vapour pressure of 0.703 atm at  $\mathbf{25}\mathbf{.}\mathbf{0}\mathbf{°}\mathbf{C}$ . What is its vapour pressure at $\mathbf{95}\mathbf{°}\mathbf{C}$  ?

What is the ${{\mathbf{\Delta H}}^o}_{\mathrm{vap}}$  of a liquid that has a vapour pressure of 621 torr at  $\mathbf{85}\mathbf{.}\mathbf{2}\mathbf{°}\mathbf{C}$ and a boiling point of  $\mathbf{95}\mathbf{.}\mathbf{6}\mathbf{°}\mathbf{C}$ at 1 atm?

Methane $\left({\mathbf{CH}}_4\right)$  has a boiling point of  $\mathbf{-}{\mathbf{164}}^o\mathbf{C}$  at 1atm and a vapour pressure of 42.8atm at  $\mathbf{-}{\mathbf{100}}^o\mathbf{C}$ . What is the heat of vaporization of  ${\mathbf{CH}}_4$?

Question: What type of forces, intramolecular or intermolecular:

1. Prevent ice cubes from adopting the shape of their container?
2. Are overcome when ice melts?
3. Are overcome when liquid water is vaporized?
4. Are overcome when gaseous water is converted to hydrogen gas and oxygen gas?

(a) Why is the heat of fusion  $\mathbf{(}\mathbf{\Delta }{\mathbf{H}}_{\mathbf{fus}}\mathbf{)}$ of a substance smaller than its heat of vaporization $\mathbf{(}\mathbf{\Delta }{\mathbf{H}}_{\mathbf{vap}}\mathbf{)}$ ?

(b) Why is the heat of sublimation  $\mathbf{(}\mathbf{\Delta }{\mathbf{H}}_{\mathbf{subl}}\mathbf{)}$ of a substance greater than its $\mathbf{(}\mathbf{\Delta }{\mathbf{H}}_{\mathbf{vap}}\mathbf{)}$ ?

(c) At a given temperature and pressure, how does the magnitude of the heat of vaporization of a substance compare with that of its heat of condensation?

Which forces are intramolecular and which intermolecular?

(a) Those allowing fog to form on a cool, humid evening

(b) Those allowing water to form when  ${\mathbf{H}}_{\mathbf{2}}$ is sparked

(c) Those allowing liquid benzene to crystallize when cooled

(d) Those responsible for the low boiling point of hexane

Name the phase change in each of these events

(a) Dew appears on a lawn in the morning

(b) Icicles change into liquid water

(c) Wet clothes dry on a summer day.

Name the phase change in each of these events:

(a) A diamond film forms on a surface from gaseous carbon atoms in a vacuum.

(b) Mothballs in a bureau drawer disappear over time

(c) Molten iron from a blast furnace is cast into ingots (“pigs”).

Explain the effect of strong intermolecular forces on each of these parameters:

(a) Critical temperature

(b) Boiling point

(c) Vapor pressure

(d) Heat of vaporization

Which forces are intramolecular and which intermolecular?

(a) Those preventing oil from evaporating at room temperature

(b) Those preventing butter from melting in a refrigerator

(c) Those allowing the silver to tarnish

(d) Those preventing ${\mathbf{O}}_{\mathbf{2}}$  in the air from forming O atoms

Which forces are intramolecular and which intermolecular?

(a) Those preventing oil from evaporating at room temperature

(b) Those preventing butter from melting in a refrigerator

(c) Those allowing the silver to tarnish

(d) Those preventing  ${\mathbf{O}}_2$ in the air from forming O atoms

Intermolecular forces are depicted in the scenes below:

(a) Name the type of force being depicted in each scene. 

(b) Rank the forces in order of increasing strength.

What is the strongest inter-particle force in each substance? 

(a) ${\mathbf{CH}}_3\mathbf{OH}$     (b)  ${\mathbf{CCl}}_4$        (c)  ${\mathbf{Cl}}_2$

Oxygen and selenium are members of Group 6A(16). Water forms H bonds, but  ${\mathbf{H}}_{\mathbf{2}}\mathbf{Se}$ does not. Explain.

Which substance has the higher boiling point? Explain. 

(a)  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}$ or  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{3}}\mathbf{ }\mathbf{ }$ (b) NO or   data-custom-editor="chemistry" ${\mathbf{N}}_{\mathbf{2}}$      (c) ${\mathbf{H}}_{\mathbf{2}}\mathbf{S}$  or  _{${\mathbf{H}}_{\mathbf{2}}\mathbf{Te}$}        

Polar molecules exhibit dipole-dipole forces. Do they also exhibit dispersion forces? Explain.

Distinguish between polarizability and polarity. How does each influence intermolecular forces?

Why are covalent bonds typically much stronger than intermolecular forces?           

How can one nonpolar molecule induce a dipole in a nearby nonpolar molecule?

Which substance has the higher boiling point? Explain. 

(a) LiCl or HCl          (b)   ${\mathbf{NH}}_{\mathbf{3}}$or   data-custom-editor="chemistry" ${\mathbf{PH}}_{\mathbf{3}}$         (c) Xe or data-custom-editor="chemistry" ${\mathbf{I}}_{\mathbf{2}}$

Sulfur dioxide is produced in enormous amounts for sulfuric acid production. It melts at  $\mathbf{-}{\mathbf{73}}^o\mathbf{C}$and boils at$\mathbf{-}{\mathbf{10}}^o\mathbf{C}$  . Its ${\mathbf{\Delta H}}^o\mathbf{fus}$ is 8.619 kJ/mol and its is 25.73 kJ/mol. The specific heat capacities of the liquid and gas are 0.995 J/gK and 0.622 J/gK, respectively. How much heat is required to convert 2.500 kg of solid ${\mathbf{SO}}_2$ at the melting point to a gas at ${\mathbf{60}}^o\mathbf{C}$ ?      

What is the strongest inter-particle force in each substance? 

(a)  ${\mathbf{H}}_3{\mathbf{PO}}_4$       (b)   ${\mathbf{SO}}_2$                 (c) ${\mathbf{MgCl}}_2$

Which member in each pair of liquids has the lower vapour pressure at a given temperature? Explain. 

(a)  ${\mathbf{HOCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}$or  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}$

(b)   ${\mathbf{CH}}_{\mathbf{3}}\mathbf{COOH}$or  ${\left({\mathbf{CH}}_{\mathbf{3}}\right)}_{\mathbf{2}}\mathbf{C}\mathbf{=}\mathbf{O}$

(c) HF or HCl

What is the strongest inter-particle force in each substance? 

(a)  ${\mathbf{CH}}_3\mathbf{Cl}$       (b)  ${\mathbf{CH}}_3{\mathbf{CH}}_3$          (c) ${\mathbf{NH}}_{\mathbf{3}}$

What is the strongest inter-particle force in each substance? 

(a)   $\mathbf{Kr}$          (b)   $\mathbf{BrF}$                  (c)   ${\mathbf{H}}_{\mathbf{2}}{\mathbf{SO}}_{\mathbf{4}}$     

Use the Figure to answer the following: 

]

a) Carbon dioxide is sold in steel cylinders under pressures of approximately 20atm. Is there liquid  ${\mathbf{CO}}_{\mathbf{2}}$ in the cylinder at room temperature ($\mathbf{~}{\mathbf{20}}^o\mathbf{C}$ )? At ${\mathbf{40}}^o\mathbf{C}$?At$\mathbf{-}{\mathbf{40}}^o\mathbf{C}$  ? At $\mathbf{-}{\mathbf{120}}^o\mathbf{C}$ ? 

b) Carbon dioxide is also sold as solid chunks, called dry ice, in insulated containers. If the chunks are warmed by leaving them in an open container at room temperature, will they melt? 

c) If a container is nearly filled with dry ice and then sealed and warmed to room temperature, will the dry ice melt? 

d) If dry ice is compressed at a temperature below its triple point, will it melt?                 

Which has the greater polarizability? Explain. 

(a) ${\mathbf{Br}}^{\mathbf{-}}$ or ${\mathbf{I}}^{\mathbf{-}}$   (b) ${\mathbf{CH}}_{\mathbf{2}}\mathbf{=}{\mathbf{CH}}_{\mathbf{2}}$  or ${\mathbf{CH}}_{\mathbf{3}}\mathbf{-}{\mathbf{CH}}_{\mathbf{3}}$   (c)   ${\mathbf{H}}_{\mathbf{2}}\mathbf{O}$or  ${\mathbf{H}}_{\mathbf{2}}\mathbf{Se}$

Which has the greater polarizability? Explain. 

(a) ${\mathbf{Ca}}^{\mathbf{2}\mathbf{+}}$ or Ca      (b)  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{3}}$or    _{${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{3}}$}        (c)  ${\mathbf{CCl}}_{\mathbf{4}}$or${\mathbf{CF}}_{\mathbf{4}}$

Which member in each pair of liquids has the higher vapour pressure at a given temperature? Explain. 

(a) ${\mathbf{C}}_{\mathbf{2}}{\mathbf{H}}_{\mathbf{6}}$ or   ${\mathbf{C}}_{\mathbf{4}}{\mathbf{H}}_{\mathbf{10}}$      (b)  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}$or ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{F}$    (c) ${\mathbf{NH}}_{\mathbf{3}}$ or  _{${\mathbf{PH}}_{\mathbf{3}}$}            

Which member of each pair of compounds forms intermolecular H bonds? Draw the H-bonded structures in each case:

(a)  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{CHOHCH}}_{\mathbf{3}}$ Or  ${\mathbf{CH}}_{\mathbf{3}}{\mathbf{SCH}}_{\mathbf{3}}$    (b)  $\mathbf{HF}$ or  $\mathbf{HBr}$

Which member of each pair of compounds forms intermolecular H bonds? Draw the H-bonded structures in each case: 

(a)  ${\left({\mathbf{CH}}_{\mathbf{3}}\right)}_{\mathbf{2}}\mathbf{NH}$or  ${\left({\mathbf{CH}}_{\mathbf{3}}\right)}_{\mathbf{3}}\mathbf{N}$    (b) data-custom-editor="chemistry" ${\mathbf{HOCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{OH}$  or ${\mathbf{FCH}}_{\mathbf{2}}{\mathbf{CH}}_{\mathbf{2}}\mathbf{F}$ 

Which forces oppose the vaporization of each substance? 

(a) Hexane    (b) Water       (c)     _{${\mathbf{SiCl}}_{\mathbf{4}}$}