Chapter 11 States of Matter Liquids and Solids 11 1 Comparison of Gases Liquids and Solids Gases are compressible fluids A gas is easily compressed because the molecules can be pushed into a smaller space A gas is a fluid because individual molecules can move easily relative to another Liquids are relatively incompressible fluids A liquid can flow Solids are rigid and incompressible Particles in a solid exist in close contact and do not move about but oscillate or vibrate about fixed sites Ideal Gas Law PV nRT Changes of State 11 2 Phase Transitions Change of State or Phase transition A change of a substance from one state to another Melting the change of a solid to the liquid state o Referred to as fusion Freezing the change from a liquid to the solid state Vaporization that change of a solid or a liquid to the vapor Sublimation change of a solid to the vapor Condensation the change of a gas to either the liquid or the solid state Deposition the change of vapor to a solid Liquefaction when a substance that is normally a gas changes to the liquid state Vapor Pressure Vapor Pressure at a given temperature the partial pressure of the vapor over the liquid measured at equilibrium Liquids and solids with high vapor pressure are said to be volatile Boiling Point and Melting Point exerted on the liquid Boiling Point the temperature at which the vapor pressure of a liquid equals the pressure As the temp of a liquid increases then the vapor pressure increase The normal boiling point of a liquid is the boiling point at 1 atm Freezing Point the temperature at which a pure liquid changes to a crystalline solid or Melting Point the temperature at which a crystalline solid changes to a liquid or melts o Melting points are affected significantly only by large pressure changes Heat of Fusion or Enthalpy of Fusion Heat of Vaporization or Enthalpy of Vaporization the heat needed for the melting of a solid the heat needed for the vaporization of Heat of Phase Transition freezes a liquid Clausius Clapeyron Equation Relating Vapor Pressure and Liquid Temperature Delta H is heat of vaporization 11 3 Phase Diagrams Phase Diagram of a substance are stable Melting Point Curve a graphical way to summarize the conditions under which different states Every point on the curves indicates experimentally determined temperatures and pressures at which two states are in equilibrium In most cases the liquid state is less dense than the solid in that case the melting point curve leans slightly to the right Vapor Pressure Curves for the Liquid and the Solid Triple Point the point on a phase diagram representing the temperature and the pressure at which three phases of a substance coexist in equilibrium Critical Temperature and Pressure Super critical fluid only one fluid called this above a certain temperature and above the critical pressure there is Critical Temperature longer exists regardless of the pressure Critical Pressure the vapor pressure at the critical temperature the temperature above which the liquid state of a substance no o The minimum pressure applied to a gas at the critical temperature to liquefy it 11 4 Properties of Liquids Surface Tension and Viscosity Surface Tension the energy required to increase the surface area of a liquid by a unit Surface Tension amount Viscosity Viscosity the resistance to flow that is exhibited by all liquids and gases o Ex Syrup is a viscous liquid 11 5 Intermolecular Forces Explaining Liquid Properties Intermolecular Forces Three types of attractive forces are known to exist between neutral molecule the forces of interaction between molecules o Dipole dipole forces o London or despersion forces o Hydrogen bonding forces Van Der Waals Forces dipole and London forces Dipole Dipole Forces general term for those intermolecular forces that include dipole Dipole Dipole force polar molecules to align themselves such that the positive end of one molecule is near the negative end of another an attractive intermolecular force resulting from the tendency of Can t exist in nonpolar molecules London Dispersion Forces London forces Dispersion the small instantaneous dipoles that occur because of the varying positions for the electrons during their motion about the nuclei the weak attractive forces between molecules resulting from London forces tend to increase with molecular mass o Because molecules with larger molecular mass usually have more electrons and long forces increase in strength with the number of electrons o Also larger molecular mass often means larger atoms which are polarizable Polarizable more easily distorted to give instantaneous dipoles because the electrons are farther from the nuclei Intermolecular Forces and the Properties of Liquids When the intermolecular forces in the liquid are strong you expect the vapor pressure to be low Liquids with weak intermolecular forces have low boiling points Surface tension tends to increase with the strength of attractive forces o If London forces are the dominant attractive forces then surface tension should increase with molecular mass Increasing the attractive forces in a molecular increases the resistance to flow Hydrogen Bonding Hydrogen Bonding a weak to moderate attractive force that exists between a hydrogen atom covalently bonded to a very electronegative atom X and a lone pair of electrons on another small electronegative atom Y o X and Y are usually the atoms F O or N Molecules that have the OH group are subject to hydrogen bonding Molecules with greater forces have lower vapor pressures 11 6 Classification of Solids by Type of Attraction of Units There are 4 different types of solids o Molecular o Metallic o Ionic o Covalent Types of Solids Molecular Solid intermolecular forces o Ex Ice Metallic Solid Ionic and covalent can be interchangeable a solid that consists of atoms or molecules held together by surrounding sea of electrons metallic bonding solid that consists of positive cores of atoms held together by a o Ex Iron copper silver Ionic Solid attraction of opposite charges ionic bonds a solid that consists of cations and anions held together by the electrical Covalent Network Solid a solid that consists of atoms held together in large networks or chains by covalent bonds o Ex Diamond graphite asbestos Physical Properties Molecular solids tend to have low melting points Melting points of covalent network solids are generally quite high If the lattice energy of a substance is greater than the higher the