CHEM 120 Lecture Notes - Lecture 14: Buoyancy, Contact Angle, Surface Tension
15 Jun 2018
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CHEM 120: LIQUIDS, SOLIDS, PHASE CHANGES
Viscosity: liquids resistance to flow, high viscosity → high IF
- Cohesive forces create internal friction within the liquid; more cohesive forces, higher IF
- Liquids are less viscous than solids
- Cohesive Forces: water and water (H bonding), pulls the wter up the sides of the container
(strong)
- Adhesion: IF between water and the surface, convex meniscus (weak)
Viscosity by Ball drop: drag fore stokes’ la, fore of graity, uoyat fore → ball bearing
- Terminal V → a=0 the forces are equal, FB+FD=Fg
When KE is higher, it disrupts IF:
- Viscosity of liquids DECREASE when the temperature increases, because at high temp these
interactions are weaker
- Hot water makes a higher pitch noise than water, the molecules have more energy so the
stikiess is ore, the isosity ad IF akes a differee to soud
Surface Tension: energy required to increase the surface area of a liquid
- The stronger the forces between the particles, the higher the surface tension
- Y =
- Surface molecules experience a net attraction towards the bulk; molecules have higher PE than
the ones in the bulk → liquids try to lower their PE so the surface of the water bends to
minimize SA
Dispersion forces increase with larger and more polarizable molecules
- The stronger the attractive forces between the molecules, the higher the BP is
The longer the molecule is; the more it can interact with molecules like itself
- Spherical molecules experience less dispersion forces because it has less contact points
- More elongated → More surface area → dispersion forces increase
Capillary Action:
- The ability of a liquid to flow against gravity; spontaneously rising in a narrow tube
- Capillary Rise: directly related to the adhesive/cohesive actions
o Fluid flows up because ATM pushes on the column and the rise reacts to balance
Wetting: ability for a liquid to spread on a surface (e.g. glass and water, coating slide), interactions are
weaker with the oil, the glass will beat up → the contact angle tells us the degrees of the contact forces
- No beating with water and glass, the adhesion forces are strong
- 180angle, no beating because the adhesion forces are weak, and the cohesive forces are
strong
- Metallic Bonding > H bonding > Dispersion > Dipole-Dipole
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