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THE MCAT-CHEM 3
EQUILIBRIUM & KINETICS
| Question | Answer |
|---|---|
| Equilibrium | forward rxn rate = reverse rxn rate --> conc. of P and R is constant |
| What does Keq ONLY vary with? | temperature |
| K > Q | shift right --> too many reactants |
| K < Q | shift left --> too many products |
| K = Q | Equilibrium |
| In a closed flask, what is constant and what varies? | volume constant, pressure varies |
| In a closed piston, what is constant and what varies? | pressure constant, volume varies |
| Exothermic rxn | R --> P + heat |
| Endothermic rxn | R + heat --> P |
| What is the unit for rate? | Molarity / second |
| The rate law deals with products / reactants? | reactants |
| What is the rate-determining step? | slowest step |
| What is the rate of the whole reaction? | rate of the rate-determining step |
| Can you isolate a transition state? | NO |
| What is the peak of the energy profile for a reaction? | transition state |
| What happens with transition state? | bonds that are going to form are just beginning to form, bonds that are going to break are just beginning to break |
| What is activation energy? | energy it takes to push reactants up to transition state |
| Enthalpy | Measure of total energy of a system |
| Arrhenius equation | k = A*e^(-Ea/RT) |
| What does Arrhenius equation tell us? | At a low activation energy and high temperature, produces a larger k --> faster reaction |
| Kinetic product has ____ Ea and is formed at _____ temperature. Thermodynamic product has ______Ea and is formed at _____ temp. | -lower / lower -higher / higher |
| What are characteristics of kinetic control? | irreversible conditions, rate, low temp, fastest reaction |
| What are characteristics of thermodynamic control? | equilibrium, reversible conditions, higher temp |
| Does kinetic / thermodynamic produce more stable product? | thermodynamic |
| What are the 2 factors that influence outcome of reaction? | stability of products (thermodynamic) and rate of product formation (kinetic) |
| What is thermodynamics concerned with in general? | whether a reaction will occur --> spontaneous or not |
| When will a rxn occur faster? | lower Ea |
| What are factors of enthalpy and entropy that favor a rxn? | exothermic and positive entropy |
| What are factors of enthalpy and entropy that don't favor a rxn? | endothermic and negative entropy |
| Enzymes/catalysts speed up the... | forward and reverse reaction |
| Catalysts and enzymes alter the ______ not the ______. | kinetics / thermodynamics |
| What are biological catalysts? | enzymes |
| T/F: Catalysts increase k. | TRUE |
| T / F: Catalysts increase Keq | False |
| Can catalysts alter position of equilibrium? | NO --> can only help achieve equilibrium faster |
| What law is the basis for the equilibrium constant? | Law of Mass Action |
| What does the equilibrium constant show? | forward rxn = reverse rxn |
| What are 2 ways for getting Keq? | -Keq equation -delta Go = -RTln(Keq) |
| Keq > 1 | more products present at equilibrium |
| Keq = 1 | equilibrium --> amt of products = amt of reactants |
| Keq < 1 | more reactants are present at equilibrium |
| Q vs. Keq | Q is the same as Keq except Q can be used for ANY point in rxn not just equilibrium |
| Does adding or removing solids or liquids to a rxn do anything? | NO --> will do nothing as long as rxn is at equilibrium |
| Decrease pressure, where does rxn shift? | towards side that makes more moles of gas |
| Does an intermediate have a finite / infinite lifetime? | finite |
| When is the intermediate in its highest concentration? | after the start of the reaction and BEFORE the rate-determining step of the rxn |
| transition state vs. intermediate | transition state is an intermediate with no measurable lifetime |
| heterolytic vs. homolytic bond cleavage | -heterolytic = both electrons in a bond go to more eN atom -homolytic = one electron goes to each atom (free radical) |
| Is more energy required to do a heterolytic or homolytic bond cleavage? | heterolytic |
| In a gas phase, are free radical carbons or carbocations more stable? | free radical carbons |
| A constant reaction rate describes a ______ order rxn. | zero |
| A gradually diminishing rxn rate is observed with a _____ order rxn. | first |
| Does an endothermic rxn increase or decrease rxn rate? | decrease because it absorbs heat --> cools the rxn and decreases heat energy |
| Higher energy product is associated with an endothermic / exothermic rxn? | endothermic |
| To monitor rate of rxn, one must monitor appearance of _____ and disappearance of _____. | product / reactant |
| What makes a good l.g. (bulkier or less bulky)? | bulkier |
| Does changing the temp. affect the energy levels of transition states? | NO --> only affects free energy of the system |
| What does adding solvent do to the concentration of a species in solution? | lowers concentration for ALL species in solution --> concentration of any species in rate-determining step is reduced |
| Will a catalyst disappear? | NO --> it will be recycled |
| catalyst lowers the activation energy for BOTH | forward and reverse rxns |
| Steady state equlibrium | rate of formation = rate of consumption |
| In what type of system does equil. occur? | closed system |
| Does a shift ever regenerate as much was lost? | NO |
| Equilbrium constants, if you double the equation, then what do you do to Keq? | square it |
| How can Keq be calculated from Ptotal? | shift in reaction (x) is equal to change in pressure from initial to final |
| A piston maintains constant? | pressure |
| Does adding a pure solid or pure liquid affect equilibrium? | NO |
| Will adding an inert gas affect equilibrium? | NO |
| Does catalyst affect position of equilibrium? | NO --> affects forward and reverse reaction |
| What to be careful of for Le Chateliers? | flexible containers --> add inert gas to rigid --> no change --> add inert gas to flexible --> dilute everything |
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