Exam 1 Gases o States of matter solid liquid gas o Gas material with no definite shape or volume move more readily N2 is the most common gas air Air N2 O2 H2O Ar He CO2 O3 CH4 o What kind of substances are gases Mostly small molecules Some free elements H2 O2 Ar Noble gases N2 F2 Cl2 Br2 Hg Smells are molecules in their gas state o Microscopic characteristics Particles are randomly moving Particles will collide elastic collisions don t lose energy Particles exert pressure by bouncing off walls Simple relationship between moles pressure volume and temperature PV nRT o Microscopic Properties Gases are compressible Lower density than solids of liquids Completely mix no immiscible gas o Units of Pressure Pressure F A Force Area SI units of Area m2 SI units of Force N N m2 1Pa Atmospheric Pressure at sea level 101 kPa 1atm 760 torr 1atm 760 mm Hg Relationship of physical properties of gas V P inverse proportion o V 1 P o V k 1 P where k constant o VP k o Boyle s Law V1P1 V2P2 V T o V T o V1 T1 k V2 T2 No change in pressure o Charles Law V1 T1 V2 T2 V n n of moles o V n o Avogardro s Law V1 n1 V2 n2 No change in P or T The number of moles does not change by substance PV nRT o R ideal gas constant 0 082057 Latm molK o See Figure 1 o Density of a Gas Much lower than liquids or solids g L or g cm3 D PM RT M molar mass o Dalton s Law of Partial Pressure 1801 Total pressure of the mixtue of gases is equal to the sum of their individual pressures Implies that P depends on the total number of moles not the chemical nature Ptot Pa Pb Pc Ptot ntotRT V If you have two gases ntot na nb Ptot na nb RT V o Kinetic Molecular Theory of Gases Gas molecules are separated by large spaces Random motion with collisions Average kinetic energy of gas particles is proportionate to the gas s temperature U 3RT M Where U average of the square of speeds and M molar mass Average speed depends on T and molar mass RMS root mean square o Gas Diffusion Gradual mixing of 2 gases randomly Graham 1832 at a constant pressure and temperature the rate of diffusion of gases is inversely proportional to the square of M r1 r2 M1 M2 r rate M molar mass Lighter gas diffuses more quickly o Gas Effusion Process by which gas escapes out of a tiny opening in a container Graham s law works here too o Ideal Gas Assumptions no attractions between molecules stickiness assume that the molecules have no volume This is where the real gas law comes in Intermolecular Forces o Forces that hold molecules together o Not bonds Only forces attractions Dipole dipole Attraction between and on different molecules two polar molecules Dipole induced dipole Between 2 different substances 1 polar and 1 non polar Ex the dipole of water repels electrons to make a dipole on C2H6 London Dispersion Forces LDF Occur between all molecules Aka induced dipole induced dipole and Van der Waals Forces Weak Relatively insignificant Hydrogen Bonding not a bond The IMF between and H atom on an N F or O and its attraction to the lone pairs of electrons on another N F or O atom o N F and O are the smallest and most electronegative If there is hydrogen bonding there are dipole dipole attractions C H never involve hydrogen bonding because they are non polar and there is no attraction o Molecular Level Solids little movement and lots of strong IMFs Liquids molecules close together but can move Gases molecules are far apart no IMF Bigger molecule more IMF s o Polarizability Ability of a molecule to react to a dipole o Polarity Similar polarities mix Similar polarity similar IMFs o Transition from liquids to gas Liquids lots of IMF Gas No IMF Liquid to gas evaporation boiling High IMF slower evaporation higher boiling point As you go down the periodic table the IMFs increase Vapor Pressure increases as the temperature of the liquid goes up Boiling point is when vapor pressure equals external pressure o Viscosity Resistance to flow in a liquid As IMFs go up the viscosity also goes up o IMFs and large molecules affect viscosity Capillary effect pulls a liquid up into a small tube paper and marker Non polar molecules will move along paper Polar molecules will stay attached to the paper Graduated Cylinder read the the bottom of the meniscus there is an attraction IMF between the water and the glass what makes the water creep up the sides Adhesive forces attraction of water to a solid Cohesive forces IMF between liquid In water and glass cohesive adhesive In mercury and glass cohesive adhesive Surface Tension o Molecules near the surface are closer together Takes extra energy to pierce a liquid surface This is because of hydrogen bonding between water molecules o Phase Diagram Pressure Temperature phase diagram for CO2 Triple point all three phases exist in equilibrium Critical Point where the liquid phase of the matter ceases to exist o Supercritical Fluid Can t tell if it is a liquid or a gas Caffeine extraction uses supercritical CO2 Supercritical water Flammable Used for extractions to remove contaminants Hard to reach 225atm Boiling Point the point where vapor pressure equals atmospheric pressure o Stronger IMFs higher boiling point o Stronger IMFs lower melting point Ionic bonds are the strongest If the slope of the line between liquid and solid is positive than the solid is more dense than the liquid If the slope of the line between liquid and solid is negative like in water than the solid is less dense than the liquid o Reason why ice floats in water Solids o Structural materials Building o o o o o Transportation Electronic materials Optical materials fiber optics Thermoelectrics Solids that get cold when conducting electricity HUGE area of research Kinds of Solids Molecular solid ice and CO2 Solid made of molecules Held together by IMFs Relatively weak Low melting points Sugar dry ice water Non conducting Ionic solids ions Made of ions NaCl Na and Cl Very high melting points Very brittle Non conducting Metallic solids metals Held together by metallic bonds Positive cations in a sea of electrons Delocalized e are responsible for metallic properties o Electrical conductivity heat conductivity and reflectivity Non directional bonding o Ductile wire malleable o Bonds rearrange but don t break Covalent networks Held together by covalent bonds into 2D infinite structures graphite or 3D infinite structures diamonds Very high melting point Very hard Usually an insulator or semi conductor Two Categories of Solids Amorphous Lacking form or shape Lacking a well defined long range