Reaction rates depend on concentration temperature and the presence of a catalyst The presence of a catalyst is the only thing that affects the Ea k can never be negative Intermediates are never used in rate laws The rate law only involves reactants and catalyst of slowest step A catalyst lowers the Ea and it speeds up the slowest step allowing it to reach equilibrium faster it DOES NOT affect the equilibrium at all The catalyst stabilizes the activated complex Rate ONLY depends on concentration so the size of the container DOES NOT matter Practice Problem Info Speed of Rate A higher concentration will take longer Even though higher concentration means higher rate the rate is faster initially however the conc still has to fall to an intended molarity The slow step is always the rate determining step In equilibrium expression DO NOT count pure solids or liquids The only thing that affects KC is temperature ALWAYS look at k values to see what the overall order is in initial rate law if need be Elementary reactions can ONLY be unimolecular A products or bimolecular A B products where two molecules are simultaneously colliding with one another If they say a percentage of a substance has degraded subtract that percentage from 100 and use that value for how much you have left e g 35 of A has degraded so 100 35 65 We have 65 of A left Le Ch telier s Principle if a system is already at equilibrium and the conditions are changed so that it s no longer at equilibrium the system will react to reach a new equilibrium in a way that partially counteracts the change Saturated system means that there is an equilibrium between the solid and the ions in aqueous solution rate of dissociation rate of the ions crashing back into the solid phase kobs would be equal to the slope key word pseudo first order and flooding The kobs would also include the reagent with the highest concentration times the rate constant k In the KC the concentrations are proportional to each other concentration of the products concentrations of the reactants Low Pressure High Volume High Pressure Low Volume More moles of gas means high pressure The equilibrium will want to shift to side with less number of moles If there are equal number of moles of gas on both sides the volume would not affect the equilibrium Temperature means that there will be fewer molecules that have enough KE to cross the Ea barrier Fast RXN small Ea Slow RXN large Ea Substitution If a slow step is not the first step then the concentrations in the rate law for the slow step must be replaced by concentrations of reactants this can be done by using the earlier reaction steps Effects of Termperature on the rate constant equation USE ARRENIHUS EQUATION Enzymes They can speed up rxns by factors of 109 to 1017 They can catalyze specific rxns because they re large molecules that bind to the reacting reactions The active site of an enzyme is the part of the molecule that carries out catalysis Only certain molecules substrates can fit in the active site and the active site can adjust its structure to accommodate the substrate and can strain bonds or bring atoms into the right position to react High temperatures cause the enzyme to become denatured by changing the enzyme structure and prevent the active site from working Heterogeneous Catalysis rnxs that take place on surfaces nitrogen and oxygen on the surface of platinum DEMO The NO molecules approach the platinum surface The NO molecules form a bond w the platinum atoms in the surface The molecules dissociate into N and O atoms w each bonded to a platinum atom The N and O atoms migrate across the surface until they get close enough to another like atom to form N2 and O2 Finally the product molecules leave the surface When reversing a reaction always take the reciprocal of the specific KC value KC vs Kp equation HIV1 Protease The active protease has monomers that are attracted to itself and the pre proteins form dimers by IFs Scientists want to inhibit the protein production of the virus The pre protein must be cut apart to become biologically active The cleavage enzyme cuts the pre protein In theory the protease can t cut the pre protein if there s an enzyme inhibitor Thrombin in cows blood did not allow the blood to clot the thrombin was the inhibitor the cleavage enzyme formed blots in the cow s blood by cutting its pre proteins forming active clots DEMO Iodine mixed w hexane and iodine mixed w H2O Essentially the same rxn As long as you have the same of moles for the products and or reactants you can start w products or reactants to get the same rxn Quantum Dots Experiment 1 Rhodamine 590 Dots flash dark and light equilibrium being fluorescent and non fluorescent They re excited by a green laser excite the rhodamine dye to a high energy state by laser and then the fluorescence goes out It goes out because the rxn occurring uses up the dark form Experiment 2 The quantum dots are more stable than the rhodamine and they also have a Bright Dark equilibrium If excited by a laser they will fade much less after continuous laser excitation The individual dots appear to be blinking They go through stages where they are bright and where they are absorbing the fluorescence Here there is NOT a rxn using up the dark form If Q KC then at equilibrium If Q KC then rxn is product favored left to right If Q KC then rxn is reactant favored right to left Equilibrium is affected by Concentration Pressure and Temperature If K is large e g 1 x 105 or K 1 products are favored If K is small e g 1 x 10 5 or K 1 reactants are favored If K is close to 1 e g 0 1 to 10 or K 1 neither the reactants nor products dominate significantly Abs lc is the slope of the Beer s law l is the cell path length 1cm c is the concentration