Understanding Physical Properties and Phase Changes

1. PHYSICAL PROPERTIES • Properties that can be measured without changing the identity of the substance. • BP, FP, (Fig 2.2) color, hardness, conductivity, solubility, density = mass/volume = m/V = g/cm3

2. PHASE CHANGES • Boiling: liquid  gas • Every substance has a specific boiling point • T < BP, substance = liquid; T > BP, substance = gas • As temp increases, vapor pressure above liquid increases. At the BP, ℓ  g is rapid and complete. • We define BP as temp at which the vapor pressure of the gas above the liquid is equal to the atmospheric pressure (atm P); Fig 2.9 • Therefore, the BP depends on atm P (e.g. baking instructions at high elevations require more time) • Condensation: gas  liquid

4. EVAPORATION • Evaporation occurs when molecules at the surface of a liquid escapes into the air because it has enough velocity to overcome attractive forces in the liquid. • Evaporation occurs when T < BP • In a open container, all of the liquid will evaporate • In a closed container, an equilibrium is established between ℓ and g. Fig 2.8

6. OTHER PHASE CHANGES • Freezing (ℓ  s) & Melting (s  ℓ) • Sublimation (sg) & Deposition (gs) • At FP, ℓ  s; two phases are in equilibrium with each other; dynamic equil. OTHER PHYSICAL CHANGES • Solubility involves the dissolution of one substance in another to form a homogeneous solution