CH14: CHEM. KINE. Flashcards
Zero-Order Rxns - Integrated Rate Law
[A] = -kt + [A]
Chemical Kinetics
study of factors affecting the rxn rate
Ectotherms
animals whose blood temperature matches the environmental temperature
what is rxn rate/rate of rxn?
(∆ concentration)/(∆ time)
simple rate/avg. rate
∙ -[∆A/∆t] or +[∆A/∆t]
for rct, the simple rate/average rate is..
(-) cuz it’s being used to create product over time
for products, the simple rate/average rate is..
positive (+) cuz it’s increasing by using reactants over time
rxn rate
(-1/a)[∆A/∆t] or +(1/a)[∆A/∆t]
[elem. or cmp.]
the M (molarity) of the elem. or cmp.
instantaneous rate in terms of chemistry
change in concentration at one particular time
relationship btwn the rxn rate and concentration of rcts
directly proportional
3 ways to monitor rxn mixtures
polarimetry, spectrometry, and pressure measurement/total pressure
polaritmetry
measuring the change in the degree of rotation of plane-polarized light caused by 1 components over time
spectrophotometry
measuring the amount of light of a particular λ absorbed by 1 component over time
total pressure
equal to the partial pressures of the rxn
aliquots - definition and method
samples (from the rxn mixture) drawn off at specific times and analyzed quantitatively
gas chromatography
separation method using gas flow through a glass or metal column that separates cmps. based on both volatility (material that can easily evaporate) and interaction w/ (l) stationary phase
methods to determine concentration in mixtures
spectrophotometry and gas chromatography
rate law
a mathematical description of how rate of rxn/rxn rate relate to concentration of rcts
provide the general rate law for A → products
Rate = k∙[A]ⁿ
k in rate law
rate constant and needs to be calculated
ⁿ in rate law
order w/ respect to the rct
overall order
total of all exponents added up
what is the rxn order with respect to NO from the equation: Rate = k[NO]²[O₂]?
2nd order
what is the overall order of the equation: Rate = k[NO]²[O₂]?
3rd order
order of rxn - mathematically
method of initial rates (rate₁/rate₂)
Integrated Rate Law
mathematical description tha relates time of rxn to the concentration of A (rct)
Zero-Order Rxns - Rate Law
Rate = k∙[A]⁰ or Rate = k
First-Order Rxns - Rate Law
Rate = k∙[A]¹ or Rate= k∙[A]
Second-Order Rxns - Rate Law
Rate = k∙[A]²
Second-Order Rxns - Integrated Rate Law
(1/[A]) = kt + (1/[A]₀)
First-Order Rxns - Integrated Rate Law
ln[A] = -kt + ln[A]₀
Zero-Order Rxns - Half-life
t(₁/₂) = ([A]₀/(2k))
First-Order Rxns - Half-life
t(₁/₂) = (ln(2)/(k))
Second-Order Rxns - Half-life
t(₁/₂) = (1/(k[A]₀))
Zero-Order Rxns - Units of k
(M/s)
First-Order Rxns - Units of k
(1/s) or s-¹
Second-Order Rxns - Units of k
(1/M∙s) or M⁻¹∙s⁻¹
order of rxns - graphically
∙R² =1 or the best fit line
Activation Energy
E needed to convert rcts to transition state (activated complex)
Half-life, t(₁/₂)
time in which the concentration of rct is halved and is dependent on order of rxn
Activated Complex
chemical species (kind of atom, molecule, ion, or particles) w/ partial bonds (partially broken and partially formed)
Frequency
of molecules that begin to transition in a given period of time
Arrhenius Equation - Definition
showing the relationship between k, rate constant, to temp.
Arrhenius Equation - Equation
k = Ae^(-Ea/(RT)) = pze^(-Ea/(RT))
Arrhenius Equation - Requirement
T in K (Kelvin)
relationship between activation E and rxn rate
inversely proportional
relationship between temp. and exponential factor in Arrhenius Equation
directly proportional
Arrhenius Equation (in y=mx+b)
lnk = (-Ea/(R))∙(1/(T)) + lnA
Two-Point Arrhenius Equation
ln(k₁/(k₂)) = (Ea/(R))((1/(T₁))-(1/(T₂))
Collision Theory
states that atoms, ions, and molecules must collide in order to react, depending on two factors: p and the z
z
collision factor
relationship btwn frequency of effective collisions and rxn rate
directly proportional
Effective Collisions
collisions that lead to rxn
p in Arrhenius Equation
orientation factor
p < 1
e- transfer
p ≈ 1
atoms colliding
p >1
complex rct molecules
Reaction Mechanism
series of individual chemical steps that create the overall chemical rxn
Elementary Steps
steps that cannot simplify and molecules interact directly
Rct Intermediates
products in a early step and then rcts in a later step
Molecularity
of rcts particles in an elementary step
of rct particles in an elem. step
Unimolecular
1 particle
Bimolecular
2 particles
Termolecular
3 particles
Rate-determining Step
∙ slowest step in the mechanism
Rate Law of Overall Rct
expo. match coefficients
Mechanism - Validation
sum of elementary steps = overall rcts and the slow rate law matches the obs. rate law
Proposed Rate Law
slowest rate law
Catalysts
substances that affect the rxn rate, but is not consumed by the rxn
Catalysts in the Equation
consumed earlier and then made later
heterogeneous catalysts
catalysts is the diff. phase as the rct particles
homogeneous catalysts
catalysts is in same phase from the rct particles
definition of rate
change in quantity in a given time period
definition of avg. rate
change in concentrations in any particular time period
relationship btwn half-life and concentration of rct
inversely proportional
gas constant for energy-related problems
8.314 J/(molxk)
gas constant for pressure-related problems
0.08206 (Lxatm)/(molxk)
when the initial step of a mechanism is fast, you will need to…
substitute the rate law of the fast step into the rate law of the slow step
When multiple variables of diff. expo. are being multiply, you would…
add the expo. of the variables tgt
to substitute the rate law of the fast step into the rate law of the slow step, you will need to…
write out the inverse equ. of the rate law of the fast step
