CHE 116: Important Equations
CHE 116: Important Equations CHE 116
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This 10 page Study Guide was uploaded by Emily.nicole on Sunday October 11, 2015. The Study Guide belongs to CHE 116 at Syracuse University taught by in Spring 2013. Since its upload, it has received 31 views. For similar materials see General Chemistry 2 Lecture in Chemistry at Syracuse University.
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Date Created: 10/11/15
Chem nal Important Concepts Rate Law Zeroorder integrated rate law A kt Aoratek Graph A vs t 0 1st order In AtA0 kt rate kA Graph nA vs t 2nCI order aAt kt 1Ao rate kAquot2 Graph 1A vs t 0 Half life 1St order up 693k depends on rate constant 0 Zero order up Ao2k depends on initial concentration 2nd order t12 1kAo Arrhenius Equation LnkEaR x 1T InA or In k2k1 EaR 1T1 1T2 y m x X b Rate Equation for Elementary Reactions Elementary reaction Molecularity Rate Law Aljproducts Unimolecular Rate kA A Al products Bimolecular Rate kA2 2A products A B products Bimolecular Rate kAB A A B Dproducts Termolecular Rate kA2B 2A B D products A B C Dproducts Termolecular Rate kABC Catalysis 0 Temperature dramatically speeds up rate of reaction Enzymes increase rate of reactions at constant body temperature 0 Increasing temperature in industrial process requires signi cant increase in energy cost Equilibrium Constant For any balanced reaction aA bB DD CC dD Reactants products the equilibriumconstant expression is Kc C quotc D Ad products AlAaBquotb reactants If Kc is very large numerator is much larger than denominator OProducts favored at equilibrium If Kc is very small denominator is much larger than numerator Reactants favored at equilibrium If Kc is around 1 numerator and denominator nearly equal Appreciable amounts of both reactants and products at equilibrium Calculate the reaction quotient where subscript i refers to concentration value at a particular instant If QC gt KC the reaction will go to the left to get to equilibrium QC must decrease numerator smaller less products and denominator larger more reactants If QC lt KC the reaction will go to the right to get to equilibrium QC must increase numerator larger more products and denominator smaller less reactants If QC KC the reaction is at equilibrium 0 Le Chatelier39s Principle When a system in chemical equilibrium is disturbed by a change in temperature pressure or concentration the system shifts in equilibrium composition in a way that tends to counteract this change in variable increase temperature equilibrium shifts to decrease temperature increase pressure equilibrium shifts to decrease pressure increase concentration of a substance equilibrium shifts to decrease the concentration endothermic reaction delta HAopositive the amounts of products are increased at equilibrium by an increase in temperature Kc is larger at higher T exothermic reaction delta HA0 negative the amounts of products are increased at equilibrium by a decrease in temperature Kc is larger at lower T Arrhenius De nition An acid is a substance that when dissolved in water increases the concentration of hydrogen ions A base is a substance that when dissolved in water increases the concentration of hydroxide ions BronstedLowry Concept Acid base reactions are proton transfer reactions The acid is the species donating a proton the base is the species accepting the proton conjugate base pairs Amphiprotic A substance capable of acting as either an acid and a base is called amphiprotic Example The following amphiprotic species can both accept and donate protons HCO3 HSO4 0 H20 In the BronstedLowry concept 1 A base is a species that accepts protons OH is only one example of a base 2 Acids and bases can be ions as well as molecular substances 3 Acidbase reactions are not restricted to aqueous solution 4 Some species can act as either acids or bases depending on what the other reactant is 0 Strong acid is completely ionized in water 0 Strong base is completely ionized in water 0 At 25 C you observe the following conditions In an acidic solution H30 gt 10 x 107 M In a neutral solution H30 10 x 107 M In a basic solution H30 lt 10 x 107 M pH is the negative logarithm of the molar h ydroniumion concentration 0 pH logH 30 H30 antilogpH 10quotpH 0 or pH ogH H antilogpH 10quotpH pOH is the negative logarithm of the molar h ydroxideion concentration 0 pOH ogOH OH antilogpOH 10quotpOH AcidIonization Equilibria Ka productsreactants wo water Ka is the acidionization constant Ka is also called the aciddissociation constant Dilute solution of a weak acid Reaction occurs only to small extent Ka is small 0Concentration of liquid water is nearly constant 0Concentration of water is not included in expression for Ka when reactions are added the equilibrium constants are multiplied Kb for the anion of a weak acid is related to Ka for the acid Ka for the cation of a weak base is related to Kb for the base Lewis Concept of Acids and Bases an acis is an electron pair acceptor and a base is an electron pair donor CommonIon Effect shift in an equilibrium caused by addition of a solute that provides an ion that takes part in the equilibrium By Le Chatelier39s principle 0 Adding a strong acid or salt of conjugate base NaA to a solution of a weak acid will shift the acidionization equilibrium to the left 0 Percent ionization will decrease Solving equilibrium problems with common ion lnsert both acid and common ion initial concentrations in table Make approximations to solve as simple linear equation Buffers Buffer is mixture of HA and A a weak acid and its conjugate base or mixture of B and BH a weak base and its conjugate acid Buffer resists change in pH by reacting with added strong acid or base pH pKa log base acid use conjugate based for both buffers If QC lt Ksp reaction goes in forward direction No precipitation If QC gt Ksp reaction goes in reverse direction Percipitation aq S If QC Ksp reaction is at equilibrium Saturated solution London Dispersion Forces Nonpolar molecules have no dipoledipole forces Dipoledipole forces account for only 20 of total energy of interaction in polar molecules Fritz London 1930 explained weak interaction between any two molecules by quotinstantaneous dipoles occurring from the varying positions of electrons during motion about nuclei London force or dispersion force An intermolecular attractive force that arises from a cooperative oscillation of electron clouds on a collection of molecules at close range Factors that affect force shape of molecule long are usually stronger increased surface area of molecule is good increase strength with weight and larger electrom clouds are easier to polarize DipoleDipole Interactions Molecules that have permanent dipoles are attracted to each other positive end is attracted to negative only important when molecules are close together Hydrogen Bonding dipoledipole interactons experienced when H is bonded to N O or F usually very strong Critical temperature The highest temperature at which a distinct liquid phase can be formed Critical pressure The pressure required is the pressure required for liquefaction at the critical temperature Supercritical uid At temperature and pressure higher than the critical temperature and pressure liquid and gas phases are indistinguishable from each other and this state is known as the supercritical uid state Laws of Thermodynamics First Law of Thermodynamics o The energy of the universe is constant 0 AU q Wfor thermodynamic system Second Law of Thermodynamics Spontaneous processes always increase the entropy of the universe Third Law of Thermodynamics The entropy of a perfect crystal at 0 K absolute zero is zero Entropy delta 5 q revT o Melting at melting point and boiling at boiling point are isothermal processes 0Consider process where heat added or removed in nitesimally slowly to produce reversible process raising or lowering temperature of surroundings in nitesimally q rev reversible equilibrium process q fusionfor solid to liquid fusion means melting q vaporization for liquid to gas q fusion 1 m0 601 X10A3jm0273 K 2201K for melting 1 mo ice at0 Delta G as Criterion for Spontaneity Delta 6 RT an K gt 1 In K positive lGo negative spontaneous products favored Klt 1 In K negative lGo positive nonspontaneous reactants favored For K is between 0018 and 57 signi cant amounts of both reactants and produ Three processes affect the energetics of solution Separation of solute particles Separation of solvent particles New interactions between solute and solvent 0 Saturated In a saturated solution the solvent holds as much solute as is possible at that temperature Dissolved solute is in dynamic equilibrium solid solute particles 0 Unsaturated If a solution is unsaturated less solute than can dissolve in the solvent at that temperature is dissolved in the solvent 0 Supersaturated In supersaturated solutions the solvent holds more solute than is normally possible at that temperature These solutions are unstable crystallization can usually be stimulated by adding a seed crystal or scratching the side of the ask Chloro uorocarbons CFCs were used for years as aerosol propellants and refrigerants Mostly CFCl3 CF2C12 Structures of Carbon Compounds There are three hybridization states and geometries found in organic compounds sp3 tetrahedral sp2 trigonal planar sp linear Alkanes 0 The only van der Waals force is the London dispersion force 0 The boiling point increases with the length of the chain 0 Carbons in alkanes are sp3 hybrids 0 0 They have a tetrahedral geometry and 1095 degree bond angles Alkenes 0 This creates geometric isomers which differ from each other in the spatial arrangement of groups about the double bond Aromatic Compounds In aromatic compounds unlike in alkenes and alkynes each pair of pelectrons does not sit between two atoms 0 Rather the electrons are delocalized this stabilizes aromatic compounds Functional Groups parts of organic molecules Where reactions tend to occur Chiraity carbons With four different groups attracted to them are handed or chiral these are optical isomers or stereoisomers if one stereoisomer is righthanded its enantiomer is lefthanded Polymers and Plastics OPolymers molecules of high molecular mass made by sequentially bonding repeating units called monomers Naturally occurring polymers wool leather silk natural rubber Synthetic polymers from controlled chemical reactions Plastic materials formed into shapes by heat and pressure Thermoplastic materials can be reshaped and recycled OThermosetting plastics shaped irreversibly OElastomer is elastic or rubbery regains original shape 0 Addition polymers are made by coupling the monomers by converting piebonds Within each monomer to sigmabonds between monomers 0 Condensation polymers are made by joining two subunits through a reaction in Which a smaller molecule often water is also formed as a byproduct 0 Copolymer is formed from 2 different monomers CrossLinking chemically bonding chains of polymers to each other can stiffen and strengthen the substance naturallyoccuring rubber is too soft and pliable for many applications in vulcanization chains are crosslinked by short chains of sulfur atoms making the rubber stronger and less susceptible to degradation Bonding in Solids 4 general types of solids metallic solidsnetwork highly delocalized electrons ionic solids sets of cations and anions mutually attracted to one another covalentnetwork solidsjoined by an extensive network of covalent bonds molecular solidsdiscrete molecules that are linked to one another only by van der Waals forces in crystalline solids atoms are arranged in very regular pattern amorphous solids are characterized by a distinct lack of order in the arrangement of atoms Alloys combinations of 2 or more elements majority are metals adding a second or third element changes the properties of mixture to suit different purposes in substitutional alloys a second element takes the place of a metal atom interstitial alloy a second element fills a space in the lattice of metal atoms MolecularOrbital Approach as the number of atoms in a chain increases the energy gap between the molecular orbitals MOs essentially disappear and continuous bands of energy states result Semiconductors in the closely packed molecular orbitals in these compounds there is a gap between the occupied MOs valence band and the unoccupied ones conduction band
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