Chemistry Chapter 10 & 11

Kinetic Molecular Theory

Based on the idea that particles of matter are always in motion

Used to explain properties of solids, liquids, and gases in terms of the energy of particles and forces that act between them

Ideal Gas

hypothetical gas that perfectly fits all assumptions of KMT

KMT of gases assumptions

1. Gases consist of large numbers of tiny particles that are far apart relative to their size

2. Collisions between gas particles and between particles and container walls are elastic collisions (collisions where KE is conserved)

3. Gas particles are in continuous, rapid, random motion and therefore possess KE

4. There are no forces of attraction between gas particles

5. The temperature of gas is measure of average KE of particles

Most of the volume occupied by gas is…

empty space

KE equation

1/2mv²

All gases at the same temperature have the same…

average kinetic energy

How does speed of gas particles related to mass?

At the same temperature, lighter gas particles have higher average speeds than heavier gas particles

Ideal gas conditions

low pressure

high temperature

Gas Expansion

Gases do not have a definite shape or volume

Gases completely fill an enclosed container

Gas particles move rapidly in all directions without significant attraction between them

Gas Fluidity

Gas particles glide easily past one another because the attractive forces between them are insignificant

Gas Density

Gas density ≈ 1/1000 liquid or solid density of the same substance because gas particles are far apart

Gas Compressibility

Gas particles crowd closer together

Gas Diffusion

spontaneous mixing of particles of two substances caused by their random motion

Gas effusion

gas particles pass through tiny opening

molecules of low mass effuse faster

Gas Rate of effusio n

directly proportional to the velocity of their particles

Real gas

• all real gases deviate from ideal gas behavior

• at high pressures and low temperatures, gas is behaves like non-ideal gas

• more polar gas molecules deviate more from ideal gas behavior

Liquid

form of matter that has a definite volume and takes the shape of its container

Attractive forces liquid vs gas

attractive forces between particles in a liquid are more effective than those between particles in a gas

what causes attraction between liquid particles

intermolecular forces

LD

dip-dip

hydrogen bonding

London Dispersion forces

weak forces that result from temporary shifts in density of electrons in electron clouds

dipole-dipole forces

attractions between oppositely charged regions of polar molecules

hydrogen bonding

occur between molecules containing a hydrogen atom bonded to a small, highly electronegative atom (N,O,F) with at least one lone electron pair

Fluid

substance that can flow and take the shape of its container

Liquid Density

typically 100x denser than gas at normal atmospheric pressure

Liquid Compressibility

relatively incompressible because particles are more closely packed together

Liquid Diffusion

constant, random motion of particles causes diffusion

gradually diffuse throughout other liquid

slower than gas because liquid particles have more attractive forces that slow movement and particles are closer together

diffusion happens quicker when liquid temperature is increased

Surface tension

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

relationship between attractive forces and surface tension

higher force of attraction between particles of a liquid, higher the surface tension

capillary action

attraction of surface of a liquid to surface of a solid

tends to pull liquid molecules upward along surface and against pull of gravity

causes meniscus

meniscus

Concave liquid surface in a test tube or graduated cylinder due to capillary action

vaporization

liquid or solid changes to gas

evaporation

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

occurs because particles of liquid have different KE

freezing

liquid to solid by removing energy (heat)

liquid → solid + energy

properties of solids

particles are more closely packed

strong attractive intermolecular forces

particles vibrate in fixed positions

maintain definite shape

volume changes slightly due to change in temp or pressure

crystalline solids

consist of crystals, a substance in which particles are arranged in orderly, geometric, repeating patterns

crystals arranged in 3D arrangement called crystal structure

amorphous solid

solid where particles are arranged randomly

melting

physical change of solid to liquid by addition of energy (heat)

solid + energy → liquid

melting point

temperature at which solid because liquid

at this temp, KE of particles overcome attractive forces holding them together

amorphous solid melting point

no definite melting point bc of random arrangement

supercooled liquids

substance that retain certain liquid properties even at temperatures at which they appear to be solid

solid density

most dense bc particles are very closely packed

solid compressibility

solids are incompressible

solid diffusion

million times slower than liquid

lattice

arrangement of particles in crystal represented by coordinate system

unit cell

smallest portion of crystal lattice that shows 3D pattern of entire lattice

ionic crystals

consist of pos and neg ions arranged in regular pattern

generally group 1 or 2 metals and group 16 or 17 nonmetals or polyatomic ions

hard, brittle, high melting points, good insulators

covalent network

each atom is covalently bonded

covalent bonding extends throughout network

hard, brittle, high melting point (highest of the solids), nonconductors or semiconductors

metallic

consist of metal cations surrounded by sea of electrons

high electric conductivity bc of sea of electrons

covalent molecular

covalently bonded molecules held together by intermolecular forces

low melting points, easily vaporized, soft, insulators

nonpolar has lower melting point than polar

phase

any part of a system that has a uniform composition and properties

condensation

gas → liquid + energy

vapor

gas in contact with its liquid or solid phase

equilibrium

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

liquid-vapor equilibrium system

rate of condensation equals rate of evaporation

liquid and vapor coexist in stable state

equilibrium vapor pressure

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

increases with increasing temperature

every liquid has specific equilibrium vapor pressure at given temp

volatile liquids

liquids that readily evaporate

weak attractive forces

nonvolatile liquids

do not evaporate readily

strong attractive forces

boiling

liquid to vapor within liquid and liquid surface

boiling point

temp at which equilibrium vapor pressure equals atmospheric pressure

lower atmospheric pressure = lower boiling point

Molar enthalpy of vaporization

The amount of energy needed to vaporize one mole of a substance

measure of attraction between liquid particles

at melting and freezing points, solid and liquid are in…

equilibrium

ex: at normal atm, the temperature of a system containing ice and liquid water will remain 0 degrees as long as both ice and water are present. only after ice is melted will the additional energy increase system temp

molar enthalpy of fusion

amount of energy required to melt one mold of solid at solid’s melting point

magnitude depends on attractive forces between particles

sublimation

solid + energy → gas

when at low temp and pressure conditions, solid exists in equilibrium with gas bc liquid cannot exist

deposition

gas → solid + energy

phase diagram

graph of pressure vs. temp

shows conditions under which phases of substance exist

triple point

indicates temp and pressure at which solid, liquid, and gas coexist at equilibrium

critical point

critical temp and critical pressure

critical temp

temp above which substance cannot exist in liquid state

above this temp, water cannot be liquified

critical pressure

lowest pressure at which substance can exist as liquid at critical temp

exothermic

releases heat/energy

freezing, condensation, deposition

endothermic

process that requires heat/energy

melting, vaporization, sublimation

Celsius → Kelvin

K = C + 273

atm → mm Hg

1 atm = 760 mm Hg

atm → torr

1 atm = 760 torr

atm → kPa

1 atm = 101.3 kPa

What is Standard Temperature and Pressure equal to at 0°C

1 atm

Molar volume

one mole of any gas at STP has a volume of 22.4 L

molar volume = 22.4 L at STP

4 variables that determine gas behavior

temperature, pressure, volume, number of particles

Pressure and number of gas molecules are … related

directly (more molecules are colliding within given space)

Where does gas naturally flow?

gas naturally flows from areas of high pressure to areas of low pressure until pressure becomes equal

What creates pressure?

Changing the size of the container. In smaller containers, molecules have less room to move, therefore they hit the sides of the container more often.

What does temperature of gas increase?

increase in kinetic energy

Relationship between temperature + pressure and volume

increase in kinetic energy causes gas molecules to hit walls of container even harder, resulting in increased pressure or increased volume

Dalton’s Law of Partial Pressure

Equal amounts of gas at the same temperature and volume have equal pressure. Total pressure inside a container is equal to partial pressure of each gas.

Pt = P1+P2+P3+…

Boyle’s Law

At constant temperature, pressure and volume are inversely related

volume decreases, pressure increases

P1V1 = P2V2

Charle’s Law

volume of gas is directly proportional to Kelvin temperature if pressure is constant

temperature increases, volume increases

V1/T1 = V2/T2

Gay Lussac’s Law`

At constant volume, as temperature increases, pressure also increases (directly related)

Temperature increase means molecules collide more with walls of container to cause increased pressure

P1/T1 = P2/T2

Combined Gas Law

only applies when number of molecules stay constant but volume, temperature, and pressure change

P1V1/T1 = P2V2/T2

Ideal Gas Law Equation

PV = nRT

P - pressure

V - volume

n - number of moles

R - ideal gas constant

T - Kelvin temperature

Molar mass equation

M = mRT/PV

density equation

D = MP/RT

ideal gas constant (R)

R = 0.0821 (L*atm)/(mol*K)

R = 62.4 (L*mm Hg)/(K*mol)

R = 8.314 (L*kPa)/(mol*K)

Avogadro’s Law

an equal volume of gas at constant temperature and pressure will have the same number of molecules

V = kn

Graham’s Law of Effusion/Diffusion

for two different gases, A and B, at the same temperature:

½M_AV_A² = ½M_BV_B²

M_AV_A² / M_BV_B² = M_BV_B² / M_AV_A²

Rate of effusion of A/B = square root of M_B/M_A

What do coefficients in chemical equations for gases represent

molar amounts of substance and relative volumes in reaction