Liquids & Solids

Question 1

Kinetic-Molecular Theory

Answer 1

A theory that describes and gives reason to the states of matter, based on the concept that matter is made up of small particles which are always in motion.

Question 2

Solid

Answer 2

Particles are tightly packed together, often arranged in a regular pattern; particles vibrate in a fixed position and do not generally move in relation to one another. Solids have a distinct shape and attractive forces are far greater than the kinetic energy.

Question 3

Liquid

Answer 3

Particles are close together with no regular arrangement; particles move past each other, but remain in essentially constant contact. Liquid has less attractive force than solid, but greater kinetic energy especially when exposed to an increase in temperature.

Question 4

Gas

Answer 4

Particles are far apart with no regular arrangement; particles move independently of one another, only occasionally colliding. Attractive forces are no longer active when a substance is in this state, but the kinetic energy is at its greatest.

Question 5

Prefix, “Intra-“

Answer 5

Within

Question 6

Prefix, “Inter-”

Answer 6

Between

Question 7

Intramolecular forces

Answer 7

Forces that hold atoms together within a molecule such as the attractive forces between a hydrogen atom and an oxygen atom within the compound H2O.

These forces are much stronger than intermolecular forces.

Question 8

Intermolecular forces

Answer 8

Forces that hold molecules together as in between one H2O molecule and another H2O molecule.

Question 9

Kinetic energy

Answer 9

Energy due to motion; in chemistry, this energy provides particles with the ability to overcome attractive forces and increase distance between particles.

Question 10

Van Der Waals forces

Answer 10

The interaction due to attractive forces between neutral atoms and between individual molecules which are attributed to the interaction of electron clouds surrounding two polar systems.

There are three types of Van Der Waals forces: electrostatic, induction & dispersion.

Question 11

Dispersion forces

Answer 11

Temporary dipoles that form because of the motion of electrons which may at times be distributed asymmetrically.

These forces are most often relatively weak, however are stronger in larger and heavier molecules or molecules that are longer as they exhibit greater polarizability due to surface area.

Question 12

Dipole forces

Answer 12

Hold polar molecules together.

Question 13

Polar molecules

Answer 13

Those molecules that have an uneven distribution of electron density.

Consider an H2O molecule comparative to a batter in which one end of the molecule is more positive and the other is more negative.

Question 14

Dipole-dipole attraction

Answer 14

Occurs when the positive side of a polar molecule attracts the negative side of another polar molecule.

Question 15

Hydrogen bonding

Answer 15

Particularly strong dipole-dipole attraction which occurs when a molecule contains a hydrogen atom bonded to fluorine, oxygen or nitrogen (the three most electronegative elements).

This bond is an example of an intermolecular bond.

This bonding is said to occur in part due to hydrogens essentially naked nucleus.

Question 16

Viscosity

Answer 16

A measure of a liquids resistance to flow with gravity.

Can be measured by the rate at which a steel bearing falls through liquid or by measuring the rate at which liquid flows through a narrow tube.

Viscosity generally increases as temperature decreases.

Question 17

Cohesive forces

Answer 17

The attractive forces between molecules of the same kind such as that between water molecules.

Question 18

Surface tension

Answer 18

Attributed to cohesive forces, a phenomenon that results on the tendency of a liquids surface to resist rupture.

These may appear as uneven surfaces and/or apparent skin-like quality. This occurs because the surface of a liquid leaves some molecules exposed to air, causing them to form tighter and stronger bonds with their neighboring molecules.

Question 19

Adhesive forces

Answer 19

The attraction of molecules of one kind for molecules of a different kind.

This phenomenon explains the difference in appearance of a drop of water on a glass surface vs on a wax paper surface. With wax paper, cohesive forces are higher than the adhesive forces, making water appear like a pronounced bead upon the surface.

Question 20

Capillary action

Answer 20

When liquid flows through narrow spaces without external forces due to adhesive and cohesive properties.

Question 21

Meniscus

Answer 21

Can be either convex or concave depending on the level of adhesive force.

Water in a glass tube is an example of a fluid with a concave meniscus.

Question 22

Concave

Answer 22

A shape which curves inward.

Question 23

Convex

Answer 23

A shape which curves outward.

Question 24

Vaporization

Answer 24

The phase change of liquid transitioning into gas.

Question 25

Condensation

Answer 25

The phase change of gas into liquid.

Question 26

Dynamic equilibrium

Answer 26

A state of balance between continuing processes.

In this case we are referring to liquid in an enclosed space where the existing evaporation (or vaporization) rate comes to equal the entering condensation rate (i.e. the amount of particles leaving the fluid and turning into vapor equals the amount of particles returning to the fluid in a process of condensation).

Question 27

Vapor pressure

Answer 27

The pressure exerted by the vapor in equilibrium with a liquid in a closed container at a given temperature.

Vapor pressure can be measured by taking a small sample of a liquid and placing it in a manometer (amount of liquid and size of the container do not have an impact on pressure measurement, only the amount of time it will take for a fluid to reach equilibrium).

Question 28

What happens to vapor pressure when there is an increase in temperature?

Answer 28

An increase in temperature results in an increase in kinetic energy of its molecules ultimately resulting in an increase in vapor pressure.

Question 29

Boiling point

Answer 29

When the vapor pressure increases enough to equal the external atmospheric pressure, the liquid reaches its boiling point.

The normal boiling point of a liquid is equal to 1 atm (i.e. standard atmosphere).

Question 30

What relates a substances vapor pressure and it’s temperature?

Answer 30

The Clausius-Clapeyron equation.

Question 31

What type of process is vaporization?

Answer 31

Vaporization is an endothermic process (i.e. evaporation is cooling; when you get out of the shower and the water evaporates from your skin; the temperature of the surrounding environment decreases and the process absorbs heat).

Question 32

What type of process is condensation?

Answer 32

Condensation is an exothermic process and so the condensation of a gas causes a release of heat and the temperature of the surrounding environment to rise.

Question 33

Melting

Answer 33

Applied energy becomes large enough to partially overcome the forces holding the molecules or ions of a solid together in their fixed positions; phase change from solid to liquid occurs.

Question 34

Melting point

Answer 34

The temperature at which the vapor pressure of the liquid phase and the solid phase are at equilibrium; when phase change from solid to liquid is occurring.

Question 35

Freezing

Answer 35

Phase change from liquid to solid due to loss of heat; molecules of a liquid slow down enough that their attraction cause them to arrange into fixed positions.

Question 36

Freezing point

Answer 36

The temperature at which the vapor pressure of the liquid phase and the solid phase are at equilibrium; when phase change from liquid to solid is occurring.

Question 37

Enthalpy of fusion

Answer 37

The amount of heat required to change one mole of a substance from the solid state to the liquid state.

(*)Note: the temperature remains constant during a phase change until the phase change is complete.

Question 38

Sublimation

Answer 38

When solids transition directly into the gaseous state, bypassing the liquid state.

Question 39

Depositon

Answer 39

When a gas transitions directly into a solid, bypassing the liquid state.

Question 40

Phase diagram

Answer 40

A diagram showing the relationship between pressure and temperature as they relate to a substances various phases.

Question 41

Triple point

Answer 41

The point at which all three phases of matter are in equilibrium.

Question 42

Critical point

Answer 42

The point at which no amount of pressure will liquify gas.

Question 43

Supercritical fluid

Answer 43

Anything above the critical point in any temperature range or pressure; highly-compressed fluid that combines the properties of gases and liquids.

Similar to liquids, these fluids are capable of dissolving nonvolatile solutes.

They exhibit very little surface tension and viscosities.

They can effectively penetrate very small openings in a solid mixture and remove soluble components (e.g. supercritical carbon dioxide is used to decaffeinate coffee).

Question 44

Negative slopes in a phase diagram

Answer 44

Water is an example of a substance which has a negative slope in its phase diagram. With most substances, applying more pressure alone will only make a solid more solid, but which ice it can begin to liquify (e.g. ice skating).

Question 45

Freeze-drying

Answer 45

A process in which a completely frozen sample is placed under a vacuum in order to remove water or other solvents from the sample.

Question 46

Pure substances

Answer 46

Substances which are made of only one type of atom or one type of molecule (i.e. atoms combined chemically such as H2O or NaCl).

Although water can be considered a pure substance (when properly distilled), it is often not, especially when found in nature.

Pure substances cannot separate into two or more substances by physical means, they are homogenous.

Question 47

Pure solids

Answer 47

Have a true melting point (i.e. a precisely defined temperature) and form crystals.

Question 48

Crystalline solids

Answer 48

Solids in which the atoms, ions or molecules are arranged in a definite repeating pattern.

There are four main types of crystalline solids: ionic, molecular, metallic & covalent network crystals.

Question 49

Ionic as crystalline solid

Answer 49

Most solid at room temperature, have a high melting point, form crystals, dissolve in water and conduct electricity when in liquid or aqueous solution (but not as solids!).

Ionic solids are made up of positive and negative ions creating a strong electrostatic bond and although they are hard, they tend to be brittle (i.e. they shatter rather than bend). Many consist of a metal element with a nonmetal element.

Question 50

Molecular as crystalline solid

Answer 50

Mostly gas or liquid, held together by weak intermolecular forces resulting in a low melting and boiling point; also poor electrical conductors.

Question 51

Metallic as crystalline solid

Answer 51

Consist of metal cations surrounded by delocalized (valence) electrons making metallic crystals great conductors of electricity.

Consist of strong bonds and make up strong materials (e.g. gold, copper, zinc, etc.)

Melting points vary greatly.

Question 52

Covalent network crystals as crystalline solid

Answer 52

Make-up very strong materials such as diamond and quartz and are made up of many covalent bonds in organ orderly pattern.

Covalent network crystals have extremely high melting and boiling points and are composed of atoms, not ions meaning that they do not conduct electricity in any physical state.

Question 53

Amorphous solids

Answer 53

Noncrystalline solids which can occur when a liquid freezes before it’s molecules become arranged in an orderly pattern.

Lack long-range order of arrangement and have no sharp melting point (e.g. glass softens before melting across a temperature range).

Amorphous develops from Greek, ‘amphos,’ meaning, ‘shapeless’.