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CHEM 0120: Exam 1
half life
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the time it takes for reactant concentration to reach half of its initial value (concentration)
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rate constant
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proportionality constant in a rate law
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reaction order
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exponent to reactant concentration in rate law; shows how rate varies concentration
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intermediate
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forms in 1 step of a mechanism and is consumed in a subsequent step
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catalyst |
increases reaction rate without being consumed in the reaction
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reaction rate
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the increase in molar concentration of product of a reaction per unit time or the decrease in molar concentration of reactant per time
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overall order of a reaction
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equals the sum of the orders of the reactant species in the rate law
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integrated rate law
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mathematical relationship btwn concentration and time
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first order integrated rate law
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ln([A]t/[A]o) = -kt
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2nd order integrated rate law
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1/[A]t = kt + 1/[A]o
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zero order integrated rate law
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[A]t = -kt + [A]o
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first order half life equation
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t1/2 = ln(2) / k
OR
t1/2 = 0.693 / k
*independent of initial concentration |
2nd order half life equation
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t1/2 = 1/k[A]o
*relies on inital concentration |
zero order half life equation
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t1/2 = [A]o / 2k
*relies on initial concentration |
collision theory
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a theory that assumes that, for a rxn to occur, reactant molecules must collide with an energy greater than some minimum value and with the proper orientation.
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activation energy
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the minimum energy of collision needed for 2 molecules to react.
--catalysts (enzymes) will decrease this |
transition state theory
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explains the reaction resulting from the collision of two molecules in terms of an activated complex
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activated complex (or transition state)
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an unstable grouping of atoms that can break up to form products
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Arrhenius Equation
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the mathematical equation
k = Ae^(-Ea/RT)
which expresses the dependence of the rate constant on temperature
--named after Svante Arrhenius |
Frequency factor
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the symbol A in the Arrhenius equation, which is assumed to be constant
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2 point form of the Arrhenius equation
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ln(k2/k1) = Ea/R (1/T1 - 1/T2)
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elementary reaction
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a single molecular event, such as a collision of molecules, resulting in a reaction
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reaction mechanism
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the set of elementary reactions whose overall effect is given by the net chemical equation
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molecularity
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the number of molecules on the reactant side of an elementary reaction
1 = unimolecular
2 = bimolecular
3 = termolecular |
rate determining step
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the slowest step in the reaction mechanism
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catalysis
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the increase in rate of reaction that results from the addition of a catalyst
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Homogenous Catalysis
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is in same phase as reactants and products and is usually in gas or liquid phase.
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heterogenous catalysis
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catalyst that exists in a different phase from the reacting species
--usually a solid catalyst in contact with a gaseous or liquid solution of reactants |
chemisorption
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binding of a species to a surface by chemical bonding forces
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substrate |
the substance whose reaction the enzyme catalyzes
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chemical equilibrium
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the state reached by a reaction mixture when the rates of the forward and reverse rxns are equal
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equilibrium constant expression
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an expression obtained by multiplying the concentrations of products, dividing by the concentration of reactants, and raising each concentration term to a power equal to the coefficient in the chemical equation
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equilbrium constant Kc
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the value obtained for the eq-constant expression when equilibrium concentrations are substituted
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law of mass action
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a relation that states that the values of the eq-constant expression Kc are constatn for a particular reaction at a given temp, whatever eq concentrations are substituted
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equilibrium constant Kp
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an eq constant for a gaseous rxn in terms of partial pressures
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homogeneous equilibrium
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an equilibrium that involves reactants and products in a single phase
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heterogeneousequilibrium
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an equilibrium involving reactants and products in more than one phase
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reaction quotient
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represented by Qc
has the same form as the equilibrium constant Kc but whose concentration values are not necessarily those at equilibrium |
Le Chatelier's Principle
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states that when a system in chem equilibrium is disturbed by a change in temp, pressure, or conc', the system shifts in equilibrium composition in a way that tends to counteract this change of variable
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when adding reactants or removing products (le chatelier's)
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when more reactant is added or product is taken away, the conc' changes of either, and net reaction occurs to left to right (in the FORWARD) direction, to give a new equilibrium and more products are produced
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when adding products or removing reactants (le chateliers)
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when more product is added or some reactant is removed, the conc' will change, and the net reaction occurs right to left (in the REVERSE) direction to give a new equilibrium, and more reactants are produced
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pressure changed (le chatelier's)
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if the pressure is increased by decreasing the volume of a reaction mixture, the reaction shifts in the direction of fewer moles of gas
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temp changes (le chatelier's)
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-->for an endothermic rxn (+ΔH), the amounts of products are increased at eq. by an increase in temp (kc is larger at higher T)
-->for an exothermic rxn (-ΔH), the amounts of products are increased at eq. by a decrease in temp (Kc larger at lower T) |
Temp Changes and Le Chatelier's Principle
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-exothermic reactions: heat is a product
-endothermic reactions: heat is a reactant
-exothermic with increased temp: shift to the left to decrease heat present
-exothermic with decreased temp: shift to the right
-endothermic with increased temp: shift to the right
-endothermic with decreased temp: shift to the left |