11.2 NOTES Liquids

Liquids – state of matter with a definite volume, indefinite shape and only one free surface

Density and compression The mass of a liquid is much greater than its gaseous counterpart for a given volume therefore liquids have a higher density than gases. Liquids cannot be compressed – definite volume!

Fluidity – ­­­­­Definition – the ability to flow Gases and liquids are both fluids, but liquids are less fluid than gases. This is because liquids have stronger intermolecular attractions which interfere with the liquid molecules ability to flow. Liquids with weaker intermolecular forces will flow better than liquids with stronger intermolecular forces.

Viscosity – Definition – measure of the liquid’s resistance to flow Factors effecting viscosity – Intermolecular forces – the stronger the attractive force, the more viscous the liquid (the “thicker” the liquid) - Shape of the molecule Temperature – viscosity decreases with increasing temperature; at higher temperatures, the molecules have greater kinetic energy allowing molecules to escape the pull of the intermolecular forces.

Question – why do we use a lighter weight of oil (5W-30) in vehicles in the winter vs. a heavier weight (10W-30) in the summer? In the winter, lower temperatures increase viscosity and the lighter weight means it is more “thin” or “less viscous” so it is better when the engine starts than a “thicker” or more viscous oil would be. In the summer, higher temperatures decrease viscosity so a “thicker” (more viscous) oil is better.  

Surface tension – measure of the inward pull by particles in the liquid “skin-like” nature of a liquid The stronger the intermolecular forces, the greater the surface tension (notice the bead-like nature of the water droplet?) Surfactants – compounds that decrease the surface tension by weakening the intermolecular forces example – detergent

Volatile – Definition – evaporates readily Intermolecular forces – the stronger the attractive forces, the less volatile the liquid Vapor pressure – the more volatile the liquid, the higher the vapor pressure  

Capillary action – the ability of a liquid to flow in narrow spaces without the assistance of, or even in opposition to, external forces like gravity. cohesion – force of attraction between identical molecules adhesion – force of attraction between particles that are different in a glass cylinder, adhesive forces > cohesive forces and the result is the liquid rises along the inner walls of the cylinder