Day 142

Hi class,

You don't need to comment on this blog post. For those students in fifth period, I have summarized the last three slides below for the quiz tomorrow.

Surface Tension

• Surface tension is the energy required to increase the surface area of a liquid by a certain amount
• Stronger IMF-->greater surface tension
• Why?: stronger net downward force on surface particles
• Surfactants decrease the surface area of water by disrupting the hydrogen bonds between water molecules
• Examples: soaps, detergents

Cohesion and Adhesion

• Cohesion describes the force of attraction between identical molecules
• Adhesion describes the force of attraction between different molecules
• Some liquids for a meniscus when placed in a narrow container
• Water forms a "smiley" meniscus in a glass tube because the adhesive forces between the water and the glass are stronger than the cohesive forces between the water molecules
• Mercury forms a "frowny" meniscus in a glass tube because the cohesive forces between the mercury molecules are greater than the adhesive forces between the mercury and the glass
• Capillary action is the upward movement of liquids in extremely narrow tubes
• how?: The liquid climbs the walls of the tube due to adhesive forces, which causes the surface area of the liquid to increase. The cohesive forces cause the rest of the liquid molecules to move upward to decrease the surface area. This continues as long as gravity allows.

Solids

• According to kinetic-molecular theory, particles in solids vibrate around fixed locations due to strong IMF
• Most solids are more dense than more liquids
• Why?: stronger IMF in solids than liquids-->particles are closer together/take less space-->greater density