CH14: CHEM. KINE. Flashcards by Anna Ellis

Zero-Order Rxns - Integrated Rate Law

[A] = -kt + [A]

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Chemical Kinetics

study of factors affecting the rxn rate

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Ectotherms

animals whose blood temperature matches the environmental temperature

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what is rxn rate/rate of rxn?

(∆ concentration)/(∆ time)

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simple rate/avg. rate

∙ -[∆A/∆t] or +[∆A/∆t]

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for rct, the simple rate/average rate is..

(-) cuz it’s being used to create product over time

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for products, the simple rate/average rate is..

positive (+) cuz it’s increasing by using reactants over time

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rxn rate

(-1/a)[∆A/∆t] or +(1/a)[∆A/∆t]

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[elem. or cmp.]

the M (molarity) of the elem. or cmp.

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instantaneous rate in terms of chemistry

change in concentration at one particular time

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relationship btwn the rxn rate and concentration of rcts

directly proportional

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3 ways to monitor rxn mixtures

polarimetry, spectrometry, and pressure measurement/total pressure

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polaritmetry

measuring the change in the degree of rotation of plane-polarized light caused by 1 components over time

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spectrophotometry

measuring the amount of light of a particular λ absorbed by 1 component over time

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total pressure

equal to the partial pressures of the rxn

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aliquots - definition and method

samples (from the rxn mixture) drawn off at specific times and analyzed quantitatively

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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

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methods to determine concentration in mixtures

spectrophotometry and gas chromatography

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rate law

a mathematical description of how rate of rxn/rxn rate relate to concentration of rcts

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provide the general rate law for A → products

Rate = k∙[A]ⁿ

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k in rate law

rate constant and needs to be calculated

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ⁿ in rate law

order w/ respect to the rct

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overall order

total of all exponents added up

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what is the rxn order with respect to NO from the equation: Rate = k[NO]²[O₂]?

2nd order

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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

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