ch. 10 - states of matter

Question 1

kinetic molecular theory

Answer 1

particles of matter are always in motion

• applies only to ideal gases
• explains properties of solids, liquids, and gases in terms of the energy of particles and the forces acting between them

Question 2

ideal gas

Answer 2

a hypothetical gas that perfectly fits all the assumptions of the kinetic-molecular theory

• helium is the most likely to fit these assumptions

Question 3

assumptions of an ideal gas

Answer 3

1. Gases consist of large numbers of tiny particles that are far apart relative to their size
   □ Most of the volume occupied by a gas is empty space
2. Collisions between gas particles and between particles and container walls are elastic collisions
   □ Elastic collision: one in which there is no net loss of total kinetic energy
3. Gas particles are in continuous, rapid, random motion; therefore, they possess kinetic energy which is in the energy of motion
4. There are no forces of attraction between gas particles
5. The temperature of a gas depends on the average kinetic energy of the particles of the gas
   □ KE = 1/2 mv^2

Question 4

when do all gases have the same average kinetic energy?

Answer 4

when they have the same temperature

Question 5

properties of gas

Answer 5

○Expansion
§ Gases do not have a definite shape or a definite volume
□ They completely fill any container in which they are enclosed
§ Gas particles move rapidly in all directions (assumption 3) without significant attraction between them (assumption 4)

○ Fluidity
§ Because the attractive forces between gas particles are insignificant (assumption 4), gas particles glide easily past one another
□ Because liquids and gases flow, they are both referred to as fluids

○ Low Density
§ The density of a gaseous substance at atmospheric pressure is about 1/1000 less than the density of the same substance in the liquid or solid state
□ B/c particles are so much father apart in the gaseous state (assumption 1)

○ Compressibility
§ During compression, the gas particles, which are initially very far apart (assumption 1), are crowded closer together

○ Diffusion and Effusion
§ Gases spread out and mix with one another (even without being stirred)
□ The random and continuous motion of the gas molecules (assumption 3) carries them throughout the available space
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Question 6

diffusion vs effusion

Answer 6

diffusion:
spontaneous mixing of the particles of two substances caused by their random motion

effusion:
a process by which gas particles pass through a tiny opening
- The rates of effusion of different gases are directly proportional to the velocities of their particles
- Molecules of low mass effuse faster than molecules of high mass

Question 7

real gas

Answer 7

a gas that does not behave completely according to the assumptions of the kinetic-molecular theory

• At very high pressures and low temperatures, a gas is most likely to behave like a non-ideal gas
• The more polar a gas’s molecules are, the more the gas will deviate from ideal gas behavior

Question 8

density

Answer 8

mass per volume, the degree of compactness of a substance

Question 9

fluidity

Answer 9

the ability of a substance to flow easily

Question 10

compressibility

Answer 10

flattened or reduced in size by pressure

Question 11

properties of liquid

Answer 11

○ Relatively high density
§ At normal atmospheric pressure, most substances are hundreds of times denser in a liquid state than in a gaseous state

○ Relative incompressibility
§ Liquids are much less compressible than gases because liquid particles are more closely packed together

○ Ability to diffuse
§ Any liquid gradually diffuses throughout any other liquid in which it can dissolve
□ The constant, random motion of particles causes diffusion in liquids
§ Diffusion is much slower in liquids than in gases
□ Liquid particles are closer together
□ The attractive forces between the particles of a liquid slow their movement
□ As the temperature of a liquid is increased, diffusion occurs more rapidly

○ Formation of Solids
§ When a liquid is cooled, the average energy of its particles decreases
§ Freezing/solidification: the physical change of a liquid to a solid by removal of energy as heat

Question 12

surface tension

Answer 12

a force that tends to pull adjacent parts of a liquid’s surface together, thereby decreasing surface area to the smallest possible size

• The higher the force of attraction between the particles of a liquid, the higher the surface tension
• The molecules at the surface of the water can form hydrogen bonds with the other water, but not with the molecules in the air above them

Question 13

capillary action

Answer 13

the attraction of the surface of a liquid to the surface of a solid

• This attraction tends to pull the liquid molecules upward along the surface and against the pull of gravity
• The same process is responsible for the concave liquid surface, called meniscus, that forms in a test tube or graduates cylinder
• Capillary action happens when adhesion is stronger than cohesion
  □ Adhesion: water sticking to other things, cohesion: water sticking to itself

Question 14

vaporization

Answer 14

a liquid or solid changes to a gas

Question 15

evaporation

Answer 15

particles escape from the surface of a nonboiling liquid and enter the gas state

• occurs bc the particles of a liquid have different kinetic energies

Question 16

boiling

Answer 16

the conversion of a liquid to a vapor within the liquid as well as its surface

Question 17

crystalline solids

Answer 17

consisting of crystals (most solids are this type)

○ Crystalline solids exist either as single crystals or as groups of crystals fused together
○ Crystal structure: the total three-dimensional arrangement of particles of a crystal
§ The arrangement of particles in the crystal can be represented by a coordinate system called a lattice (unit cells)
○ Unit cell: the smallest portion of a crystal lattice that shows the three-dimensional pattern of the entire lattice

Question 18

crystal

Answer 18

a substance in which the particles are arranged in an orderly, geometric, repeating pattern

Question 19

amorphous solids

Answer 19

the particles are arranged randomly

• atoms not arranged in a regular pattern
• comes from Greek word for “without shape”

Question 20

ionic crystals

Answer 20

positive and negative ions arranged in regular patterns

□ Generally, ionic crystals form when Group 1 or Group 2 metals combine with Group 16 or Group 17 nonmetal or nonmetallic polyatomic ions
□ Electrically conductive as liquids or in aqueous solutions, but nonconductive in solid state
□ These crystals are hard and brittle, have high melting points, and are good insulators

Question 21

covalent network crystals

Answer 21

each atom is covalently bonded to its nearest neighboring atoms

□ The covalent bonding extends throughout a network that includes a very large number of atoms
□ The network solids are very hard and brittle, have high melting points, and are usually nonconductors or semiconductors

Question 22

metallic crystals

Answer 22

consisting of metal cations surrounded by a sea of delocalized valence electrons

□ The electrons come from the metal atoms and belong to the crystal as a whole
□ The freedom of these delocalized electrons to move throughout the crystal explains the high electric conductivity of metals

Question 23

covalent molecular crystals

Answer 23

consisting of covalently bonded molecules held together by intermolecular forces

□ If the molecules are nonpolar, then there are only weak London dispersion forces between molecules
□ In a polar covalent molecular crystal, molecules are held together by dispersion forces, by dipole-dipole forces, and sometimes by hydrogen bonding
□ Covalent molecular crystals have low melting points, are easily vaporized, are relatively soft, and are good insulators

Question 24

phase

Answer 24

any part of a system that has uniform composition and properties

Question 25

condensation

Answer 25

the process by which a gas changes to a liquid

Question 26

vapor

Answer 26

a gas in contact with its liquid or solid phase

Question 27

equilibrium

Answer 27

a dynamic condition in which two opposing changes occur at equal rates in a closed system

Question 28

equilibrium vapor pressure

Answer 28

the pressure exerted by a vapor in equilibrium with its corresponding liquid at a given temperature

in a closed container, the rate of evaporation equals the rate of condensation

• increases with increasing temperature, increasing the avg kinetic energy of the liquid’s molecules
• each time a gas hits the wall of a container, it exerts pressure, explaining the high pressure of gases

Question 29

volatile liquids

Answer 29

liquids that evaporate readily

• They have relatively weak forces of attraction between their particles (i.e. ether)

Question 30

nonvolatile liquids

Answer 30

do not evaporate readily

• They have relatively strong attractive forces between their particles (i.e. molten ionic compounds)

Question 31

boiling point

Answer 31

the temperature at which the equilibrium vapor pressure of the liquid equals the atmospheric pressure

• The lower the atmospheric pressure, the lower the boiling point
• At the boiling point, all of the energy absorbed is used to evaporate the liquid, and the temperature remains constant as long as the pressure does not change
• If the pressure above the liquid being heated is increased, the temperature of the liquid will rise until the vapor pressure equals the new pressure and the liquid boils once again
• Energy must be added continuously in order to keep a liquid boiling
  □ The added energy is used to overcome the attractive forces between molecules of the liquid during the liquid-to-gas change and is stored in the vapor as potential energy

Question 32

molar enthalpy of vaporization

Answer 32

the amount of energy as heat that is needed to vaporize one mole of liquid at the liquid’s boiling point at constant pressure
(liquid-gas)

• strong attraction btwn particles = high molar enthalpy of vaporization

Question 33

molar enthalpy of fusion

Answer 33

the amount of energy as heat required to melt one mole of a solid at the solid’s melting point
(solid-liquid)

Question 34

freezing

Answer 34

the physical change of a liquid to a solid

- loss of energy

Question 35

sublimation

Answer 35

the change of state from a solid directly to a gas

Question 36

deposition

Answer 36

the change of state from a gas directly to a solid

Question 37

phase diagram

Answer 37

a graph of pressure versus temperature that shows the conditions under which the phases of a substance exist

Question 38

triple point

Answer 38

the temperature and pressure conditions at which the solid, liquid, and vapor of the substance can coexist at equilibrium
- Low pressure, low temperature

Question 39

critical point

Answer 39

the critical temperature and critical pressure

• Critical temperature: the temperature above which the substance cannot exist in the liquid state
• Critical pressure: the lowest pressure at which the substance can exist as a liquid at the critical temperature

Question 40

structure of water

Answer 40

• strong hydrogen bonds
• two atoms hydrogen + one atom oxygen united by polar covalent bonds
• hexagonal arrangement of molecules IN ICE
• hydrogen bonds in ice are fewer and more disordered
• liquid water is denser than ice

Question 41

physical properties of water

Answer 41

○ At room temperature, pure liquid water is transparent, odorless, tasteless, and almost colorless
○ The molar enthalpy of fusion of ice is relatively large compared with the molar enthalpy of fusion of other solids
○ Water expands in volume as it freezes, because its molecules form an open rigid structure
§ This lower density explains why ice floats in liquid water
○ Both the boiling point and the molar enthalpy of vaporization of water are high compared with those of nonpolar substances of comparable molecular mass
§ Strong hydrogen bonds!
○ Steam (vaporized water) stores a great deal of energy as heat

Question 42

exothermic vs endothermic

Answer 42

exothermic: reaction gives off energy
endothermic: reaction absorbs energy from surroundings

Question 43

intermolecular forces

Answer 43

forces of attraction between molecules