Chemical vs. Physical Changes, Chemical vs. Physical Properties, and Matter

Phases of matter

• Gas

  • Ex: Steam

• Liquid

  • Ex: Water

• Solid

  • Ex: Ice

Phases are determined by…

• How fast particles are which determines…

• How far apart particles which determines…

• How much attraction are between particles

  • Whose more strongly attracted?

  • Close together or far apart?

  • Coulombic attractions

Characteristics of phases

• Two questions distinguish phases

  • Does it have its own definite shape or does it take the shape of its container? (can it flow? is it fluid?)

  • Does it have its own definite volume or does it take the volume of its container? (is it compressible/expandable?)

Gases

• Examples

  • Air (78% O2, 21% N2, 0.9% Ar)

  • Natural gas (95% methane, CH4)

  • Perfume essences (liquids that evaporate)

  • Butyric acid (essence of vomit)

• Speed - particles are moving very fast

• Spacing - particles are far from each other

• Attractions - particles have little to none

• Definite shape? Fluids? - no definite shape so it’s fluid

• Definite volume? Compressible/expand? - has no volume so compressible and expandable

Liquids

• Examples

  • Water, H2O (most liquids are water-based)

  • Ethanol, C2H5OH

  • Gasoline, C8H18

• Speed - Medium speed

• Spacing - Close spacing

• Attraction - Some attraction

• Definite shape? Fluids? - no shape so its a fluid

• Definite volume? Compressible/expand? - has volume so not compressible and expandable

Solids

• Examples

  • Ice, H2O (strange stuff, just like liq. H2O)

  • Metals

  • Plastics (large C-based molecules)

• Speed - very low

• Spacing - very close

• Attractions - high attraction

• Definite shape? Fluids? - has a definite shape

• Definite volume? Compressible/expand? - has volume so not compressible or expandable

Phase Changes

• Change Temp or Pressure to change

• How do you raise temp? -

• How do you raise pressure? - Squeezing

• Names of phase changes?

  • solid 🡪 liquid - melting

  • liquid 🡪 solid - freezing

  • liquid 🡪 gas - vaporization

  • gas 🡪 liquid - condensation

  • solid 🡪 gas - sublimation

Fourth phase

• Plasma - ionized gas

  • Electrons have been stripped from atoms

  • Takes a lot of energy

• Rare on earth

  • Surface of suns

  • Nuclear fusion reactors

  • Neon lights

  • Lightning

Chemical Change

• New substances created (old destroyed)

• Bonds within molecules are broken so identity of substance is new

• Atoms not destroyed, just rearranged

• New substance might mean

  • New color (burning, rusting, digestion)

  • New odor (digestion, decomposition, eggs)

  • Bubbles (new gas … sometimes)

  • Precipitate (new solid)

  • Heat in or out

Physical Change

• No new substances produced

  • No new colors, odors

• Bonds between molecules broken

• Examples

  • Phases changes (will see new gas/liquid/solid)

  • Shape change

  • Tearing, breaking

  • Dissolving

Physical vs. Chemical Properties

• Chemical properties are properties that depend on chemical change

  • Ex: Corrosion

• Physical properties are anything else

  • Ex: Intensive (identity dependent only) vs extensive (depends on size of sample)