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chem exam 2 kinetics
| Question | Answer |
|---|---|
| [] brackets represent | molarity |
| reaction rate is | change in concentration (of a reactant) per unit time a positive , time dependent (in general) quantity |
| unit of rate | mol/Ls aka mol L^-1 s^-1 |
| average rate | concentration change over a finite time interval rate of change OVER A TIME INTERVAL ex: amount of distance in a time, the average speed |
| instantaneous rate | rate of change at one moment of time concentration change over an infinitesimal interval ex:the speed @ any given moment |
| rate constant | k it does NOT depend upon the concentrations of the reactants (does depend on temp but not conc.) proportionality factor (shows that rate is proportional to concentration of ___) |
| reaction order | used to characterize rate laws the power to which the concentration of the reactants are taken phrased like: “Reaction is mth order with respect to [A] (concentration A)” |
| is the reaction order the same as/related to stoichiometric coefficients? | NO |
| overall reaction order | sum of the exponents themselves m + n + p “The reaction is __th order overall” |
| how are rate laws determined | experimentally have to take experimental data to reduce cannot be deduced stoichiometrically |
| rates are always | positive |
| reactants have what sign in front of their rate law before solving it | negative you get less of it multiple by -1 to get it positive |
| products have what sign in front of their rate laws before solving | positive you get more of it |
| are rates consistent throughout | no rate changes at different times; not 100% consistent we can use instantaneous rate eqn to find these |
| generic rate law | rate=k[A]^m[B]^n [C]^p |
| arrheinus factor | e^(-Ea/RT) the fraction, out of allmolecules, of the ones that have enough kinetic energy to overcome activation energy “represents frac of molecules with KE greater than Ea at a given temperature” shows dependance of k on T |
| exponential integrated rate law equation for first order kinetics | [A]=[A]oe^-kt |
| smaller rate constant means | rxn progresses slower |
| rearranged for [A] equation for second order kinetics | [A]= [A]o/ (1 uhhhhh idk look it up |
| t1/2 eqn fr 1st order kinetics | t1/2=ln2/k |
| t1/2 eqn fr 2nd order kinetics | t1/2=1/k([A]o) |
| t1/2 eqn for other order kinetics | t1/2= [A]o/2k |
| unit of rate constant for first order kinetics | 1/s |
| unit of rate constant for second order kinetics | L/mol s |
| unit of rate | mol/Ls |
| unit of concentraionn | for molarity, its mol/L |
| unit of rate constant in 0th order kinetics | mol/Ls |
| unit of k | depends on the order could be mol/Ls if its 0th order because k=rate and rate is that unit |
| how to find unit of k | plug units into respective rate eqn and cancel out |
| for first order what does t1/2 rely on | it DOES NOT rely on concentration of reactants it DOES depend on k, the rate constant, and it is inversely proportional. as the rate of the reaction speeds up, the half life of the reaction decreases |
| how is t1/2 related to the rate constant | for each order, k is INVERSELY proportional to t1/2 as rate increases and reaction speeds up, the half life time decreases |
| half life | time at which the concentration of a reactant has decreased to 1/2 its initial value |
| integrated rate law | can be used to calcate concentration of reactants described how reactant and product concentration depend on time (using a math eqn) |
| frequency factor | A (italic) NOT CONC how many collisions per unit time related to collision frequencies when they collide has variable units depending on the order you’re in |
| Arrhenius equation | k doesnt rely on concentration, but guess speech on temperature, this temperature dependance can be described by this equation |
| arrhenius factor | e^-Ea/RT the number of molecules that have enough kinetic energy at a given temperature to overcome the activation energy plus some “the fraction of molecules with kinetic energy greater than Ea at a given temp” |
| arrhenius equation | k=Ae^Ea/RT |
| as activation energy gets higher, what happens to the arrhenius factor? | it gets smaller see graph for it to make sense higher Ea is further right on the graph |
| as temperature increases what happens to the arrhenius factor? | it also increases! flattens the curve, can take in more water @ the same Ea |
| activation energy | minimum energy necessary to form a product during a collision/hvae a rxn |
| if - delta H, what does the curve look like? how does this relate to energy of products and reactants | reactants side is shorter; had to give some of your own to finish off the product side shorter on left then stoops down on right |
| if +delta H, what does the curve look like? how does this relate to energy of products and reactants | the left side is taller/larger, reactants |
| other name for transition state | activated complex |
| what 2 factors are needed in determining if collisions result in a reaction | 1) proper orientation 2) energetics of collision; 2 molecules must produce enough energy in their collision to overcome the activation energy of the reaction aka needs to form enough energy to reach transition state |
| transition state | NOT activation energy activated complex an energy threshold that needs to be met, via producting enough activation energy, to form products |
| how to catalysts work | they provide an alternate path with a lower activation energy kinetic energy curve flattens |
| catalysis | the increase in the rate of a reaction that results from the addition of a catalyst |
| catalyst | speeds up a reaction rate without being consumed it is “recycled” in the reaction can be used again and again creates a new pathway, one with lower activation energy and therefore lower cost at the beginning and end of a rxn mechanism (opp of inter) |
| does catalyst addition increase % yield | no you just get to the same amount faster |
| how does catalyst addition affect delta H | it doesn’t delta H stays the same |
| how does catalyst addition affect reactants and product quantities | it doesnt they begin and start at the same amount, just need less energy and costs |
| do catalysts affect overall equillibrium | no just how fast you get there |
| homogeneous catalysis | when the catalyst has the same phase as the reacting species |
| heterogeneous catalysis | catalyst has a different phase than the reactants catalyst often a solid and reactants are gaseous or liquid |
| chemisorption | reactions chemically bond to the catalyst |
| enzyme catalysis | biological organisms use a class of highly specific and efficient protein catalysts called enzymes |
| substrate | substance catalyzed by an enzyme |
| rule of thumb for effect of of temperature on reaction rate | the rate doubles for every raise in 10 degrees C |
| how does reaction rate change as contact between reactants decreases | it decreases why aq rxns proceed fast |
| how does reaction rate change with reactants concentration | as concentration increases so does rate |
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