Chemical Kinetics Flashcards
Gibbs Free Energy (delta G)
change in this determines whether a reaction will be spontaneous or non-spontaneous
Intermediate
the molecule that does not appear in the overall reaction
hard to detect as they are consumed immediately after they are formed
Rate-Determining Step
slowest step in any mechanism
Collision Theory of Chemical Kinetics
rate of a reaction is proportional to the number of COLLISIONS PER SECOND between the reacting molecules IN CORRECT ORIENTATION AND ENERGY
Activation Energy (Ea)
the minimum energy required for a reaction to take place; can be called an energy barrier
Rate of reaction Equation
rate = Z x f
Z = number of collisions per second
f = fraction of collisions that are effective
Arrhenius Equation
k = Ae ^ (-Ea / RT)
A = frequency factor
Ea - activation energy of reaction
k = rate constant of reaction
Frequency Factor/Attempt Frequency
measure of how often molecules in certain reactions collide, s^-1
can be increased by increasing the number of molecules in a reaction
Trends of Arrhenious Equation
as A increases, so too does k
as T increases, value of the exponent would be less than 1, gets more positive, k increases
Reaction Coordinate
traces the reaction from reactants to products
Transition State/Activated Complex
greater energy than both reactions and products; activation energy required to reach this state
can revert back to products or reactants WITHOUT any energy
not an actual identity, not the same as an intermediate
Free Energy Change of Reaction (deltaG rxn)
energy difference between products and reactants
Exergonic Reaction
Negative free energy change between reactants and products is energy being RELEASED
Endergonic Reaction
Positive free energy change between reactants and products is energy being ABSORBED
Activation Energy Forward/Reverse Reactions
FR: difference in free energy between transition state and reactants
RR: difference in free energy between transition state and products
Factors Impacting Reaction Rate
Reaction Concentration
Temperature
Medium
Catalysts
Reaction Rate Factor: Concentration
greater the concentration, te greater the number of collisions
increases reaction rate for all BUT ZERO ORDER REACTIONS
Reaction Rate Factor: Temperature
As temperature increases, so too will reaction rate
avg kinetic energy of particles increases to surpass Ea
Reaction Rate Factor: Medium
some molecules re more likely to react with each other in aq vs non aq environments
polar solvents are preferred as the dipole polarizes bonds of reactants and weaken the bonds to make it easier to break
Reaction Rate Factor: Catalyst
increase reaction rate without being consumed within the reaction by DECREASING ACTIVATION ENERGY (Ea)
- increase frequency of collisions
- change orientation of reactants to make collisions more effective
- donate electron density to reactants
- reduce intramolecular bonding within reactant molecules
DO NOT IMPACT Keq or the free energies of the products/reactants
DO NOT MAKE NONSPONTANEOUS REACTIONS SPONTANEOUS
Homogeneous Catalysis
catalyst is in same phase as reactants (solid, liq, gas)
Heterogenous Catalysis
catalysts us ub a ds=istinct phase
Rate of General Reaction:
aA + bB -> cD + dD
rate (M/s) =
- delta [A] / (a(delta t))
=
- delta [B] / (b(delta t))
=
delta [C] / (c(delta t))
=
delta [D] / (d(delta t))
For nearly all forward, irreversible reactions, the rate is _____ to the concentration of the reactant, with each concentration raised to some experimentally determined exponent.
proportional
Rate Law for
aA + bB -> cD + dD
rate = k[A]^x [B]^y
x and y are orders of the reaction
THE VALUES OF X and Y ARE ALMOST ____ tTHE SAME AS THE STOICHIOMETRIC COEFFICIENTS
NEVER
Rate constant (k) is only a constat for a specific _____ at a specific ____
reaction, temperature
For a reversible reaction, Keq =
Keq = k/ k^-1
(rate of forward reaction / rate of reverse)
Experimental Determination of Rate Law
1) Look At Table of Experiments
2) Find 2 trials where one of the reacts is the same and the other is different
3) Divide the rates, divide the concentrations and solve for exponent
4) do the same for the other reactant
5) solve for k using newly found exponents and experimental data trial
Zero-Order Reaction
rate of formation of product C is INDEPENDENT of changes in concentrations of any reactants A and B
rate = k (M/s)
*k is dependent on temperature so it is possible to change the rate of zero order via temp or catalyst just not concentration
Plotting Zero-Order Reaction
slope of -k straight line
First - Order Reaction
rate is directly proportional to ONLY ONE REACTANT
rate = k[A]^1 or k[B}^1
k = s^-1
ex: radioactive decay
Radioactive Decay 1 Order
rate = - delta [A] / (a(delta t)) = k[A]
First Order Reaction Concentration Substance
[A]t = [A]o e^ -kt
A first order rate law with a SINGLE reactant suggests that a reaction begins when the molecule undergoes a…..
chemical change by itself without any chemical or physical interaction
Plotting First-Order Reaction
Conc vs time will make a curve that is non linear
taking ln[A] vs time, a linear line is made where slope = -k
Second Order Reaction
rate is proportional to either the concentrations of two reactions or the squared concentration of a single reactant
rate = k[A]^1[B]^1 or k[A]^2 or k[B]^2
second order suggests a physical collision between two reactant molecules, especially if the rate is: rate = k[A]^1[B]^1
Plotting Second-Order Reaction
plot 1/[A] vs time and get a linear line with slope = k
There are few high order reactions because…
ut us rate for three particles to collide together with the correct orientation and enough energy
Mixed Order Reactions
non-integer orders (fractions) that apply to reactions with rate orders that vary over the course of a reaction
Broken Order
the fraction orders for mixed order reactions
