chapter 12

What are the three phases of matter?

1. solid

2. liquid

3. gas

In which phase are the molecules/ atoms furthest apart?

gas phase.

In which phase are the molecules/ atoms closest together?

solid phase.

What are intermolecular forces (IMF)?

attractive forces between molecules

Where do IMFs exist?

in all molecules/ atoms

What are intramolecular forces?

“bonds;” attractive forces within molecules

The state of matter depends on the relative magnitudes of what?

1. thermal energy present

2. IMFs present

What is thermal energy associated with?

the random motion of molecules and atoms in matter

What is the relation of thermal energy and IMF in gases?

thermal energy is large relative to IMF

What is the relation of thermal energy and IMF in liquids and solids?

thermal energy is small relative to IMF

What is the density of gases compared to liquids and solids?

very low compared to liquids and solids

What is the compressibility of gases?

very compressible bc their particles are far apart

What kind of shape do gases have?

assume shape of container

What is the strength of IMFs in gases?

very weak due to large distances between particles

What is the density of liquids compared to gases and solids?

have a high density relative to gases but are slightly less dense than solids

What is the compressibility of liquids?

slightly compressible

What kind of shape do liquids have?

assume shape of container

What is the strength of IMFs in liquids?

moderately strong IMFs

What is the density of solids compared to gases and liquids?

have a very high density relative to gases and slightly higher density than liquids

What is the compressibility of solids?

very difficult to compress a solid

What kind of shape do solids have?

have a rigid structure

What are the two types of shapes for solids?

1. crystalline

2. amorphous

What is a crystalline shape?

has a specific, ordered arrangement of particles (ie. diamond)

What is an amorphous shape?

random arrangement of particles (ie. graphite)

What is the strength of IMFs in solids?

very strong IMFs

When going from solid to liquid and liquid to gas, what do you do?

heat it

When going from gas to liquid and liquid to solid, what do you do?

cool it

When going from gas to liquid (without changing temperature), what do you do?

compress it to increase pressure

How does pressure change affect solids?

does not affect solids as they are already compressed

Why are propane tanks examples of pressure change in relation to phase changes?

propane tanks are under pressure to keep the propane a liquid. when you open the tank, the escaping propane turns to gas.

How do ionic bonds result?

attraction of opposite charges

What state has a weak IMF?

gas

What state has a moderate IMF?

liquid

What state has a strong IMF?

solid

What do IMF result from?

the interactions between charges, partial charges, and temporary charges on molecules, atoms, or ions involving dipole-dipole forces, hydrogen bonds, and London dispersion forces.

What do bonds result from?

the attraction of opposite charges; LARGE charges at CLOSE distances

What do IMFs result from?

SMALL charges at LARGE distances

What are the four main types of IMFs?

1. Dispersion (weakest)

2. Dipole-dipole

3. hydrogen bonding

4. ion-dipole (strongest)

What are dispersion forces?

“London forces” or “Van Der Waals forces”

present in ALL atoms/ molecules

dispersion forces are the result of random movement of electrons in atoms and molecules

What is a dipole?

measurement of separation of positive and negative charges

What does the strength of a dispersion force depend on?

polarizability (how easy electrons moved) of electrons in an atom or molecule

What is the trend for dispersion forces and molar mass?

dispersion forces get stronger as molar mass increases

a larger molecule has more electrons that are further from the nucleus, which makes them easier to move

What is the relationship between IMFs and melting/ boiling points?

stronger IMFs result in higher melting and boiling points due to increased energy required to overcome these forces

How does shape influence the strength of dispersion forces?

more elongated shapes have greater surface area, leading to stronger dispersion forces compared to spherical shapes bc IMFs can occur all along the chain, so it has more and stronger IMFs interactions → higher melting and boiling points

What does it mean if a molecule has a dipole?

it has a negative and positive end

What forces will be present if a molecule is polar?

dipole-dipole as well as dispersion forces

What properties are affected by the presence of dipole-dipole forces?

melting and boiling points

If two compounds have similar molecular weights, and one has dipole-dipole forces while the other does not, which has a higher m/bp?

polar molecule will have higher m/bp because of stronger IMF

What other property does polarity also affect?

miscibility of two or more liquids

What is miscibility?

the ability of liquids to mix without separating into two phases

What kind of compounds do polar compounds dissolve?

polar compounds

What kind of compounds do non polar compounds dissolve?

non polar

What is hydrogen bonding as an IMF?

stronger than dipole-dipole; occurs when hydrogen atom is bonded directly to oxygen, nitrogen, or fluorine atom
ie. HF, HO, HN

When do you use molar mass to justify strength of IMF?

when things in comparison have only dispersion forces

What are ion-dipole forces?

strongest IMF; requires two different compounds

occurs between an ionic compound and polar compound

What three properties do intermolecular forces influence?

1. surface tension

2. viscosity

3. capillary action

What is surface tension?

the tendency of liquids to minimize surface area

In a liquid container, where is surface tension the strongest?

at the surface

this attraction provides a skin on the surface due to the attraction of molecules inward

stronger IMF → stronger surface tension

What is viscosity?

the resistance of a liquid to flow

What three things does viscosity depend on?

1. size/ shape of molecules

2. IMF

3. temperature

How does size/ shape affect viscosity?

longer/ more complicated molecules are more viscous

How do IMFs affect viscosity?

stronger IMF, stronger viscosity

How does temperature affect viscosity?

higher temperature, less viscous as there is more energy to overcome the IMFs

What is capillary action?

the ability of a liquid to flow up a narrow tube against gravity

What two forces result in capillary action?

Cohesive and adhesive forces

What are cohesive forces?

the IMF attractions between liquid molecules

What are adhesive forces?

the IMF attractions between liquid molecules and wall of tube

What occurs when cohesive < adhesive?

the liquid molecules are more attracted to the tube than they are themselves, so the liquid is drawn up the tube → capillary action

What occurs when cohesive > adhesive?

the liquid molecules are more attracted to themselves, so no capillary action occurs

Since molecules in a liquid are in constant motion due to thermal energy, what is the average energy of the molecules?

the higher the temperature, the greater the average “energy” of the molecules, but at any point in time, some molecules have more energy and some have less energy than the average

What is vaporization?

liquid → gas

occurs when you have enough energy to overcome IMFs

What is condensation?

gas → liquid

a gas molecule comes in contact with liquid and is overcome by IMF

How much energy is needed for surface molecules to become gas molecules compared to inner molecules?

molecules at the surface have fewer neighbors attracting them and holding them together, so less energy is needed for these molecules to break the IMF to become gas molecules

Why does a glass of water eventually disappear if condensation and evaporation occur at the same time?

once a molecule has vaporized, it isn’t likely to come back in contact with liquid, so the rate of vaporization is greater than the rate of condensation

What three things affect the rate of vaporization?

1. temperature

2. IMF

3. surface area

How does temperature affect the rate of vaporization?

provides energy for molecules to overcome IMF (to enter gas phase)

How do IMFs affect the rate of vaporization?

the weaker the IMF, the greater the rate of vaporization

How does surface area affect the rate of vaporization?

a larger surface area has more surface molecules, so it has a greater rate of vaporization

What kind of a reaction is vaporization?

endothermic; energy must be supplied to overcome the IMF

What kind of a reaction is condensation?

exothermic; releases heat

What is a steam burn?

occurs when water condensates on your skin, releasing heat

What is sweating?

occurs when your body uses heat to vaporize water

What is the heat of vaporization?

∆H_vap; the amount of heat required to vaporize one molecule

What does the magnitude of the heat of vaporization depend on?

temperature

ie. water boils at 100 C

takes 40.7 kj/mol to vaporize at 100 C and 44 kj/mol at 25 C

What must occur for vaporization to occur for liquids at lower temps?

liquids at lower temperatures require more energy to vaporize, as their temperature needs to be raised to the boiling point before it can vaporize