Physical & Chemical Properties, Changes, and Separation

Physical vs. Chemical Properties

• All matter exhibits properties classified as either physical or chemical.
• Physical property: observed/measured without altering substance’s identity.
• Chemical property: describes ability to undergo a change producing new substances.

Key Physical Properties

• Appearance: color, luster, clarity.
• Mechanical: hardness, malleability, ductility.
• Thermal: melting point, boiling point.
• Electrical/thermal conductivity.
• Density (mass-to-volume ratio).
• Solubility and miscibility.

Key Chemical Properties

• Reactivity with acids, bases, oxygen, water, etc.
• Flammability and combustibility.
• Corrosion/oxidation tendencies (e.g., iron rusts).
• Decomposition or fermentation behavior.

Physical vs. Chemical Changes

• Physical change: no bonds broken/formed; same particles before & after.
  • State change, dissolution, separation, deformation.
• Chemical change: bonds broken/formed; produces matter with new identity.
  • Combustion, oxidation, fermentation, decomposition.

Evidence of Chemical Change

• Temperature change (exothermic/endothermic) without external heating.
• Light emission.
• Unexpected color change.
• Gas formation (bubbling not due to boiling).
• Precipitate formation from clear solutions.
• Odor change.

Reversibility

• Many physical changes are reversible (freeze–melt, condense–evaporate).
• Chemical changes typically hard to reverse without another chemical reaction.

Classifying Examples

• Water boiling → physical.
• Salt dissolving in water → physical (retrievable by evaporation).
• Nail rusting → chemical (new substance, color change).
• Two clear solutions forming yellow solid → chemical (precipitate & color).

Separating Mixtures (Physical Processes)

• Distillation: separates components via volatility differences.
• Fractional distillation: multiple boiling points (e.g., crude oil refining).
• Filtration: separates solids from fluids using a porous barrier.
• Other methods: decantation, centrifugation, chromatography (not detailed here).

Quick Comparison Chart

• Physical property: luster of gold; Chemical property: iron corrodes.
• Physical change: ice melting; Chemical change: paper burning.