CHEM 1120 Edition 1nd Exam 3 Study Guide Chapters 19 20 24 Chapter 19 Word or Concept Definition Explanation Spontaneous process A chemical or physical change that is thermodynamically favored by nature i e ball rolling downhill does not mean it is fast can be temperature dependent not all spontaneous processes are exothermic Reversible process A process that can be reversed by an infinitesimal change in a variable returns both system and surrounding to their original state Irreversible process Process which is not a reversible process can only return system to its original state but not the surroundings 2nd Law of Thermodynamics S universe S system S surroundings 0 for reversible process 0 for irreversible 0 Entropy Measure of disorder in a system measure of the extent to which a system s energy is not available to do work S k x ln W S q rev T Positional Entropy A gas will spontaneously expand into a vacuum probability 1 2 n where n is number of molecules Entropy as energy disposal Energy will try to disperse over a large number of particles and energy levels S k x ln W W number of possible microstates K Boltzmann constant 1 381 x 10 23 J K Entropy and Solutions Usually when a solid is dissolved in a solvent entropy increases Entropy of perfect crystal at 0 K is Equal to 0 Standard Molar Entropies So Positive for pure substances doesn t 0 So gas So liquid So solid higher molar mass higher So More atoms in molecule higher So So Sum of So products Sum of So reactants Same for Gibbs free energy except use Go S universe S rxn H rxn T When T and P are constant G H TS State function Spontaneity and Gibbs Free Energy Negative forward reaction spontaneous 0 at equilibrium Positive Reverse reaction spontaneous G w max Equals maximum useful work that can be done by the system at constant T and P G Go RTlnQ Q value of equilibrium expression under ANY conditions Go RTlnK At equilibrium Chapter 20 Word or Concept Definition Explanation Electrochemistry Relationship between chemical change and electrical work Electrochemical cell Systems that incorporate a redox reaction to produce or utilize cell energy Does work by releasing energy from spontaneous reaction Does work by absorbing energy from a source of electricity Oxidation Loss of electrons Reduction Gain of electrons Oxidizing agent Species that does the oxidizing taking electrons from substance being oxidized gets reduced Reducing agent Species that does the reducing giving electrons to substance being reduced gets oxidized Half Reaction Method Acids 1 Separate into 2 half cells 2 Balance all elements except O and H Half Reaction Method Bases Voltaic Cell galvanic cell balance O using H20 balance H using H balance charge using e3 Multiply by factors to equate e loss and gain 4 Add balanced half reactions 1 Balance as if it were acidic steps 1 4 above 2 Neutralize H by adding OH to both sides 3 Cancel H2O where necessary Uses spontaneous chemical reaction to produce electrical energy Electrolytic cell Uses electrical energy to drive a non spontaneous reaction G 0 Anode Where oxidation occurs Zn Zn2 2e Cathode Where reduction occurs 2e Cu2 Cu Electron flow Leave anode and flow through wire into cathode as electrons reach cathode cations are attracted to now negative cathode Voltaic Cell notation Oxidation on left reduction on right vertical line implies a phase boundary double vertical line implies a salt bridge Not all voltaic cells have salt bridges could have porous barrier Cell potential Electrical potential difference between 2 half cells also called voltage electromotive force emf or Ecell for spontaneous reaction 0 Difference between 2 electrodes Standard cell potential Eocell Cell potential when operated under standard conditions 1 atm 1M pure liquids and solids and usually 298 K Eo cathode Eo anode More positive cathode Volt SI unit of potential 1 J C G nFEcell or Go nFEocell n moles of electrons transferred F Faraday 9 65 x 10 4 C mol charge of a mole of electrons Eocell RT nF lnKeq Ecell Eocell RT nF ln Q R 8 314 J mol K T temp in Kelvin n moles of electrons transferred F 9 65 x 10 4 Q reaction quotient Fuel cells Convert hydrogen and oxygen into electricity and heat no recharging not a battery Corrosion of Iron Iron dissolves anodic region Fe2O3 H20 rust created needs air Cathodic protection Make iron behave more like cathode use galvanized steel coated with a sacrificial layer of zinc zinc oxidized instead of iron Electrolytic cell Energy from an external source drives a nonspontaneous reaction Overvoltage Difference between the actual cell potential required for appreciable electrolysis and the calculated cell potential Chapter 24 Alkanes Single covalent bond Alkenes At least one double bond Alkynes At least on triple bond Aromatics Contain rings with delocalized electrons Acyclic alkanes No rings CnH2n 2 saturated hydrocarbons Condensed structure Atoms usually drawn next to atoms to which they are bonded parentheses are used around similar groups bonded to the same atom Skeletal structurs Carbon atom at junction of any two line or end of line assume enough hydrogens around each carbon to make it tetravalent draw in heteroatoms Structural isomers Same molecular formula different bond connectivities Cyclic alkanes Contain only C and H in single covalent bonds at least one ring CnH2n Classification of Carbon atoms Primary bonded to one other carbon secondary 2 other carbons tertiary 3 other carbons quaternary 4 other carbons Naming Prefix location and name of substituents Root number of carbons in longest chain suffix what family Naming alkanes ane name longest continuous chain number the longest chain starting at end nearest a substituent name each substituent alkyl group use di tri tetra if 2 or more alkyl groups are identical list alkyl groups in alphabetical order 10 roots based on number of carbons 1 meth 2 eth 3 prop 4 but 5 pent 6 hex 7hept 8 oct 9 non 10 dec Alkyle groups Carbon substituent bonded to a long carbon chain formed by removing one H from an alkane to name change ane of parent to yl Reactions of Alkanes Rather unreactive make great nonpolar solvents undergo combustion reactions Acyclic Alkenes Contain at least 1 double bond no rings CnH2n unsaturated hydrocarbons Geometric isomers Result from restricted rotation around bonds same molecular formula and bond connectivity but differ in spatial arrangement Cis isomer 2 substituents on the same side of a double bond Trans Two substituents on opposite sides of a