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THE MCAT-CHEM 3

EQUILIBRIUM & KINETICS

QuestionAnswer
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
Created by: 507935299