Chemistry Unit 10

States of matter

kinetic theory of matter

all matter consists of tiny particles that are in constant, random motion

kinetic energy

energy of motion (depends on the mass and speed of particles)

temperature

measure of the average KE of the particles in a substance

kinetic theory of gases

1. gas particles have negligible volume and are very far apart

2. gas particles are in constant, random motion

3. gas particles have elastic collisions (no energy is lost and no attractive forces)

gas pressure

the result of gas particles colliding (with walls of a container)

• more collisions = more pressure

• causes: more particles, decreased volume, higher temperature

pressure

atmospheric pressure is caused by the force (weight) of air due to gravity

standard atmospheric pressure

air pressure at sea level

• equal to 1 atm, 760 mmHg, or 101.3 KPa

• 0C and 1atm

intermolecular forces

forces of attraction between molecules (not as strong as intramolecular forces)

london dispersion forces

attractive forces caused by uneven distribution

diople-diople forces

attractive forces between polar molecules

hydrogen bonding

special type of diople-diople forces occurring between hydrogen and an electronegative element (O, N, F)

evaporation

transition of particles from liquid to gas at a temperature below the boiling point (temp of remaining liquid decreases as evaporation occurs)

criteria for evaporation

must be at the surface of the liquid and must have enough energy to break IMFs

vapor pressure

pressure exerted by gas particles above a liquid (result of evaporation)

vapor pressure and IMFs

the weaker the attractive forces, the higher the vapor pressure (more volatile liquid)

boiling

rapid phase transition from liquid to gas (vapor)

• bubbles form due to vapor pressure being equal to atmospheric pressure

normal boiling point

the temperature liquid will boil at when the vapor pressure above the liquid is 1 atm (760 mmHg)

melting point

the temperature a solid changes into a liquid

• strong IMFs lead to higher melting points

• vibrations between particles need to become strong enough to overcome attractions

freezing point

the temperature a liquid changes into a solid

• melting point = freezing point

• at this temp, liquid and solid phases are in equilibrium

amorphous solids

lack an ordered internal structure (atoms are randomly arranged)

crystal structure

particles are arranged in a crystal lattice

unit cell

the smallest group of particles within a crystal that retain the geometric shape (determines the overall crystal shape)

allotropes

2 or more different molecular structures of the same element

• each allotrope has different physical properties due to its different structure

• only a few elements have allotropes (phosphorous, sulfur, oxygen, boron, antinomy)

gas

low density, indefinite shape and volume, weak IMFs

liquid

high density, indefinite shape but definite volume, moderate IMF

solid

high density, definite, shape and volume, strong IMFs

water

• water does not follow the normal trend for density of solids, liquids and gases

• solid ice is less dense than liquid water

• unique that water is a liquid at room temperature (due to H-bonding) other molecular substances with similar molar masses are gases at room temperature

melting

solid to liquid (endothermic = particle absorb energy)

freezing

liquid to solid (exothermic = particles release energy)

boiling (vaporation)

liquid to gas (endothermic)

condensation

gas to liquid (exothermic)

sublimation

solid directly to gas

deposition

gas directly to solid

phase diagram

shows the phase of a substance at different temperatures and pressures

the curves are lines of equilibrium (2 phases at once)

critical point

the temp. and pressure at which the gas and liquid phrases of a substance become identical

triple point

the temperature and pressure at which all 3 phrases are in equilibrium (all 3 exist at the same time)

supercritical fluid

a substance held at or above its critical temperature and pressure

has properties of both gas liquid