Solids and Liquids Chapter 14 Chem B

Condensed States Attractive forces (interparticle) cause matter to hold together as liquids or solids Gases – particles are spread out and very fast – attractions minimized by motion When temp. drops, molecules SLOW and….

Condense – change from gas to liquid Because the attractions between molecules become greater. Particles start sticking together…liquid

Particles compared

Vaporization Opposite of condensation Boiling and evaporation - two types Boiling – details later Evaporation – happens only at surface and to highest energy molecules (they escape!) - leaves lower energy particles behind – this means lower temp. (cooling via sweat)

Liquids and Solids Liquid particles slide past each other, but are close together. Solids have stronger attractions. Particles go slower and get “locked” into a crystal lattice. Motion is vibrational, not free. Freezing is change from liquid to solid Melting is opposite of freezing.

Liquid and Solid

Sublimation Change from solid directly to gas. Dry ice is best example. Ice and iodine also. Deposition is opposite process.

Crystalline Solids Particles in fixed, orderly, repeating pattern. Crystal Lattice Usually higher energy needed to break up Means higher MP Bonding in all directions Most solids including salt, sugar, and all solid metals

Amorphous Solids Wax, Glass, and some plastics Particles are randomly arranged, not evenly spaced. Melting point is not sharply defined

Vapor Pressure In a closed container all liquids will have some evaporation This produces vapor pressure. Amount depends on the temp. and the type of liquid Nonpolar substances have highest VP High temp. gives high VP

Vapor pressure curve graph

Boiling Boiling is the liquid to gas phase change Occurs when the VP = atmospheric pressure Boiling point is the temp. when VP = Standard Pressure

Boiling can happen at different Temperatures Change the vapor pressure. Pressure cookers (higher BP) Demo…..?

KE and PE in phase changes During a phase change, temperature remains constant →KE constant, PE changes Energy is used to change arrangements of particles not speed. During heating/cooling, temperature changes → KE changes, PE is constant

Heating Curve for Water and Ice Ice Water and Steam Steam -20 20 40 60 80 100 120 220 760 800 Heating Curve for Water PE change KE Change KE Change Temp C PE change KE Change Time

Calculating energy changes Three equations: 1. For temp. change: ΔH= mCΔT 2. For liquid-solid change ΔH = m ΔHfus 3. For liquid-gas change ΔH = m ΔHvap In all these ΔH is the energy change; m is mass; ΔT is temp change Other values are constants.

Phase diagrams