7978163
Descripción
Fichas por Christine Luk, actualizado hace más de 1 año
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Creado por Christine Luk
hace casi 8 años
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| Pregunta | Respuesta |
| Surface Energy | = Surface tension high E = high T = low stability disruption of intermolecular bonds |
| water surface energy | E = 0.072 J/m^2 T = 0.072 N/m |
| Surface phenomena rule: minimization of E (Surface free energy) | reduce SA only expose low E areas alter geometry to reduce E |
| Surface Phenomena (3 types) | (1) surface adsorption (2) surface reconstruction (3) surface reactions |
| surface reconstruction types (2) | crystalline polymer orientation |
| Surface reactions (3) | oxidation passivation diffusion |
| Absorption | like a sponge penetration molecules into bulk of material |
| Absorbate | material being absorbed |
| Absorbent | material which is absorbing e.g., activated carbon, ion exchange resin |
| Adsorption | adhesion on to surface |
| Absorption phenomena: Principle 1 | High Energy surfaces are quickly coated by lower energy species e.g. water on glass/metal/oxide hydrocarbons on inorganic surfaces surfectants on air/water interface |
| Detergent mechanism | 1. soap decreases T of water, >wet 2. soap disperses grease as micelles 3. greasy micelles in suspension to be washed away soap has hydrophilic (- charge) heads, hydrophobic tails |
| Physisorption | unbalanced atomic molecular forces on surface attract gases and molecules absorbate weakly adherant via secondary interactions (van der waals) < 0.25eV/surface site Eads = 0.1eV/mer |
| Chemisorption | at high temps, unbalanced surface forces electron share/valence bond with gas atoms strong modifications to electron structure/density of absorbate molecule > 0.5eV/surface site |
| physisorption, chemisorption and temperature | low T: high physisorption high T: high chemisorption same surface can be physisorption at low T and chemisorption at high T |
| Absorption phenomena | high energy surface in principle one (which covered by weaker species) is relative to surrounding medium in H2O environments, hydrophilic material has lower E / T than a hydrophobic one eg. absorption/denaturing proteins happens easily on hydrophobic surfaces in H2O environment |
| -OH -CH3 which is hydrophillic, hydrophobiic, polar or nonpolar | -OH = hydrophilic, polar -CH3 = hydrophobic, nonpolar |
| Metal oxidation steps | one scenario: 1) physisorption 2) molecular oxygen dissociates and reduces by chemisorption 3) bond rearrangement resultant reduction in surface energy |
| Metal oxidation reaction | |
| passivation | depositing layer of oxide on surface requirements: small kp (less air, slower oxidation) adherent oxide (mustn't detach) |
| Galvanic Corrosion | 2 metals in contact where Va > Vb so, B becomes sink (electrons flow A to B) |
| Stainless steel | steel allow with min 10.5% chromium content by mass does not readily corrode/rust/stain with H2O as ordinary steel |
| Corrosion reaction | |
| corrosion | destructive result cehm reaction betw metal/metal alloy and environment |
| aqueous corrsion | electronic charge transfer i.e., electrochemical reaction typically metal acts as anode & cathode can be acidic/neutral/basic environment |
| Chemisorption Oxide reactions | |
| Acid/Base Oxide Reactions |
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