Chapter 11 Concepts

Question 1

Fundamental difference between states of matter is…

Answer 1

… the distance between particles.

Question 2

Condensed phases

Answer 2

Liquids and solids

* Because particles are closer together

Question 3

The state a substance is in at a particular temperature and pressure depends on two antagonistic entities:

Answer 3

• The kinetic energy of the particles.

* The strength of the attractions between the particles.

Question 4

Gas - characteristic properties

Answer 4

• Assumes both volume and shape of its container
• Expands to fill its container
• Is compressible
• Flows readily
• Diffusion within a gas occurs rapidly

Question 5

Liquid - characteristic properties

Answer 5

• Assumes shape of portion of container it occupies
• Does not expand to fill its container
• Is virtually incompressible
• Flows readily
• Diffusion within a liquid occurs slowly

Question 6

Solid - characteristic properties

Answer 6

• Retains own shape and volume
• Does not expand to fill its container
• Is virtually incompressible
• Does not flow
• Diffusion within a solid occurs extremely slowly

Question 7

Intramolecular bonds (covalent bonds) are: strong/weak?

Answer 7

Strong

Question 8

Attractions between molecules (intermolecular bonds) are: strong/weak?

Answer 8

Weak

Question 9

Physical properties that are controlled by intermolecular attraction

Answer 9

• Boiling point
• Melting point
• Vapor pressure
• Viscosity

Question 10

van der Waals forces (what are they)

Answer 10

Intermolecular forces, collectively

Question 11

van der Waals forces (3)

Answer 11

• Dipole–dipole interactions
• Hydrogen bonding
• London dispersion forces

Question 12

London dispersion forces (describe)

Answer 12

(or, dispersion forces), are attractions between an instantaneous dipole and an induced dipole
* Electrons on atoms or molecules, even if nonpolar, tend to cause electrostatic attraction between other atoms or molecules due to electrons being repelled to one side (instantaneous dipole), exposing a positive side, which in turn attracts electrons on the other atom or molecule (induced dipole)

Question 13

Polarizability

Answer 13

The tendency of an electron cloud to distort into dipoles, whether in polar or nonpolar molecules.

Question 14

Factors Affecting London forces

Answer 14

• Shape of the molecule. The greater the surface area (long & skinny vs. round), the greater the dispersion forces.
• Molecular weight. Larger atoms have larger electron clouds that are easier to polarize.

Question 15

Dipole-dipole Interactions (describe)

Answer 15

• Molecules that have permanent dipoles are attracted to each other.
• The positive end of one is attracted to the negative end of the other, and vice versa.
• These forces are only important when the molecules are close to each other.

Question 16

Effect of molecular polarity on the boiling point

Answer 16

The more polar the molecule, the higher its boiling point.

Question 17

Which Have a Greater Effect: Dipole–Dipole Interactions or Dispersion Forces?

Answer 17

• If two molecules are of comparable size and shape, dipole–dipole interactions will likely be the dominating force.
• If one molecule is much larger than another, dispersion forces will likely determine its physical properties.

Question 18

Hydrogen bonds (describe and explain)

Answer 18

• The dipole–dipole interactions experienced when H is bonded to N, O, or F.
• Hydrogen bonding arises in part from the high electronegativity of nitrogen, oxygen, and fluorine. Also, when hydrogen is bonded to one of those very electronegative elements, the hydrogen nucleus is exposed.

Question 19

Ion-Dipole Interactions (describe)

Answer 19

• Positive ends of polar molecules are attracted to negatively-charged anions.
• Negative ends of polar molecules are attracted to positively-charged cations.
• Is what makes it possible for ionic substances to dissolve in water (ions are surrounded by water molecules).

Question 20

List all 5 forces in ascending order of strength of the bond

Answer 20

• Dispersion forces only
• Dipole-dipole forces
• Hydrogen bonding
• Ion-dipole forces
• Ionic bonding

Question 21

Viscosity (definition and description)

Answer 21

• Resistance of a substance to flow (the ease with which molecules can move past each other).
• Increases with stronger intermolecular forces and decreases with higher temperature.

Question 22

Surface tension (definition and explanation)

Answer 22

• The net inward force experienced by the molecules on the surface of a liquid.
• On surface molecules, there is no upward force to cancel the downward force, so each molecule feels a net “downward” pull.
• On interior molecules, there is pull in all directions, so each molecule feels no net pull in any direction.

Question 23

Heat of fusion

Answer 23

The energy required to change a solid at its melting point to a liquid.

Question 24

Heat of vaporization

Answer 24

The energy required to change a liquid at its boiling point to a gas.

Question 25

Heat of sublimation

Answer 25

The energy required to change a solid directly to a gas.

Question 26

Effect of phase change on temperature

Answer 26

• The heat added to the system at the melting and boiling points goes into pulling the molecules farther apart from each other.
• The temperature of the substance does not rise during a phase change.

Question 27

Vapor Pressure (defined)

Answer 27

• At any temperature some molecules in a liquid have enough energy to break free.
• As the temperature rises, the fraction of molecules that have enough energy to break free increases.

Question 28

Effect on pressure from increasing vaporization

Answer 28

Pressure increases as more molecules escape the liquid

Question 29

Describe liquid and vapor dynamic equilibrium

Answer 29

Liquid molecules evaporate and vapor molecules condense at the same rate.

Question 30

The boiling point of a liquid is the temperature at which its vapor pressure equals…

Answer 30

… atmospheric pressure.

Question 31

The normal boiling point is the temperature at which its vapor pressure is (in torr)…

Answer 31

…760 torr

Question 32

Clausius–Clapeyron equation

Answer 32

Vapor pressure is inversely proportional to its temperature.

P = −(delta)Hvap/RT + C where C is a constant

Question 33

Liquid Crystals (defined)

Answer 33

An intermediate state where liquid crystals have some traits of solids and some of liquids for substances do not go directly from the solid state to the liquid state.

Question 34

Liquid Crystals - liquid state

Answer 34

Molecules are arranged randomly

Question 35

Liquid Crystals - Nematic liquid crystalline phase

Answer 35

Long axes of molecules aligned, but ends are not aligned.

Question 36

Liquid Crystals - Smectic A liquid crystalline phase

Answer 36

Molecules align in layers, ends aligned, perpendicular to layer planes

Question 37

Liquid Crystals - Smectic C liquid crystalline phase

Answer 37

Molecules align in layers, ends aligned, inclined to layer planes