GChem: Kinetics & Equilibrium (GOOD review) Flashcards
When given a bunch of reactions that proceed after each other, how do you tell what the intermediate is? Catalyst? Are transition states shown in mechanisms?
Intermediate -> Molecule generated then consumed
Catalyst -> Consumed then regenerated, conc doesn’t really change
Transition states not shown
How to determine what the rate determining steps is:
What 3 factors determine a fast rate?
The slowest step in a process determines the overall reaction rate
a) The lower Ea (catalyst) (pg 187 the second bump in reaction coordinate diagram was higher - greater Ea- so it is the rate determining step) b) At higher temp, more reactant molecules have a sufficient energy to overcome Ea and molecules collide at a higher frequency c) The greater concentrations of reactants, the faster the rxn rate bc favorable collisions with proper orientation of the colliding molecules (catalyst fix substrate!!) is more likely as the concentrations of reactant molecules is higher
Activated complex
Transition state
When proper Activation E is present and rxn can proceed, the reactants can reach high E (and short lived) transition state, also called the activated complex
Label reaction coordinate diagram
What do the peaks rep? what does the hole in middle rep? Where is Ea? Where is delta G?
pg. 187
Does ΔG thermo or kinetics?
MCAT LOVES TO MIX THESE TWO TO TRICK YOU
THERMO!
How to determine is something is a catalyst by looking at rxn steps
The catalysts is consumed but reformed at the end of the rxn
Does catalyst affect ΔG, ΔH, ΔS?
Catalyst does NOT affect ΔG, ΔH, ΔS bc catalyst is kinetics but ΔG, ΔH, ΔS is thermo!
Rate law, what do coefficients rep? *How is it determined and exceptions? Units for each part of equation
k? What is the order? What is rate law based on? What is included in rate law?
Rate law based on rate-determining step (slowest step) and is determined EXPERIMENTALLY not from orders of reactants
Exception to this rule is for an elementary step in a reaction mxn
The rate law is first order for a unimolecular elementary step (one molecule reactant makes one molecule product) and second order for a bimolecular elementary step (two molecules combine to make one product)
A and B are reactants
rate = k[A]^x[B]^y
x -> the order of the rxn with respect to A
y -> the order of the rxn with respect to B
(x + y) = overall order of the reaction
k = the rate constant (units can change)
units for rate law M/s
Solids and solvents (liquid) not included in rate law
For MCAT -> order is 0, 1, or 2
*How to determine orders of reactants based on experiment?
How do we get rate constant?
f = c^x
f -> reaction rate increases by a factor of f
c -> the concentration of a reactant increases by a factor of c
x -> the order
We get rate constant by just plugging into the rate law we found using any experiment from the table
*What is the Arrhenius equation (likely don’t need to know just the relationships)? How are k and Ea, T related? Literally logic
The rate will increase by a factor of ____ for every 10º C increase in temp
k = Ae^-(Ea/RT)
k is directly proportional to T (not linear)
k is indirectly proportional to Ea
Which makes logical sense
factor of 2 to 4
What are the units of the rate on the left side of the rate equation?
If If Rate =k[A][B], the units of the rate constant k must be____
If the rate were third order, the units would be____, or if first order then simply ___
M/s
If If Rate =k[A][B], the units of the rate constant must be M-1s-1
If the rate were third order, the units would be M-2s-1, or if first order then simply s-1
What factor affects both kinetics and thermodynamics?
Temperature
What can you have a solution of?
Anything
ex. 2 gases
Like dissolves like
Solutes will dissolve best in solvents where the IMF being broken in the solute are being replaced by equal (or stronger) IMF between solvent and the solute
Why is electrolyte called an electrolyte?
Bc due to the free ions, the solution can conduct electricity
Why is electrolyte called an electrolyte?
What is the van’t Hoff factor for almost all biomolecules (hormones, proteins, steroids)?
What type of molecules are the best electrolytes?
Bc due to the free ions, the solution can conduct electricity
i = 1
Ionic compounds are the best type of electrolytes
Which of the following is the weakest electrolyte
a) NH4I
b) LiF
c) AgBr
d) H2O2
H2O2 is covalent compound
Dynamic equilibrium
Chemical equilibrium
Where are we in the process when we have reached molar solubility?
Dynamic equilibrium:
When forward and reverse rates are equal
When we have reached molar solubility of the solute for that particular solvent (saturated), and the reverse process of dissolved form of the solute are said to be in dynamic equilibrium
Chemical equilibrium:
Online -> occurs when the number of particles becoming products is equal to the number of particles becoming reactants
Online: What is difference between molarity and concentration?
Molarity -> moles solute/ Liters solution (volume)
Concentration -> grams/Liter
**ON MCAT
3 phase solubility rules
- what happens to solubility of solids in liquids as increase temp, sol of gases in liquids as increase temp. sol of gases in liquids as increase pressure?
- The solubility of solids in liquids tends to increase with increasing temp (sugar in hot tea)
- The solubility of gases in liquids tends to decrease with increasing temperature (warm coke)
- The solubility of gases in liquids tends to increase with increasing pressure
**ON MCAT
Salt Solubility Rules (3)
1) All Group I (Li+, Na+, K+, Rb+, Cs+) and ammonium (NH4+) salts are soluble
2) All nitrate (NO3-), perchlorate (ClO4-), and acetate (C2H3O2-) salts are soluble
3) All silver (Ag+), lead (Pb2+/Pb4+), mercury (Hg2 2+/Hg2+) salts are insoluble, except for their nitrates, perchlorates, and acetates
How to determine a salt’s molar solubility (solubility calculation), what does it mean, units?
When a solution is saturated, it is at _____
What is solubility product?
x -> mol/L or M
Molar solubility is the maximum concentration
salt’s molar solubility = the number of moles of that salt that will saturate a liter of water/ the amount of substance that can dissolve in a specific solvent at a specific temperature
pg. 215
Mg(OH)2 (s) -> Mg2 (aq) + 2OH- (aq)
x -> x + 2x
OH- is 2x bc Mg(OH)2 splits into 2 OH-
so Ksp = (x)(2x)^2
Then will be given Ksp and solve x
When a solution is saturated, it is at equilibrium
Solubility Product (Ksp) -> K for solid dissociation
What does sp mean? What do these values PHYSICALLY MEAN?
When Qsp > Ksp
When Qsp = Ksp
When Qsp < Ksp
When Qsp soluton saturated
When Qsp>Ksp -> excess salt will precipitate
Common ion effect
When a rxn is added which dissociates and then has a common ion that the OG rxn has, this causes a shift left for the OG equation bc now there are more reactants than products
**ΔG’º < 0; Keq___1 and ___ are favored
ΔG’º = 0; Keq___1 and ___ are favored
ΔG’º > 0; Keq___1 and ___ are favored
ΔG’º < 0; Keq > 1 and prod are favored
ΔG’º = 0; Keq = 1 and neither are favored
ΔG’º > 0; Keq < 1 and reactants are favored
**What factors can change K?
ONLY temperature
**What is Keq? How to calculate it, what is included in equation? Value calculated using ____ concentrations
What does K>1, K=1, and K<1 mean? How does it related to Q and what does this relationship tell us and what do we observe with each relationship? What is Q?
If Qsp > Ksp, what do you get?
What is Keq dependent on? What can you do for calculating keq with gases?
**Keq is the condition the reaction will try to achieve, describes the position of the equilibrium
K>1 means at equilibrium favors products
k=1 at equilibrium favors neither
K<1 at equilibrium favors reactants
Keq = [C]^c[D]^d / [A]^a[B]^b
coefficients become powers
Value calculated using EQUILIBRIUM concentrations
exclude pure solids and liquids, and super dilute solutions
Aqueous things included
Q is the reaction quotient when reaction is not at equilibrium
Comparing Q to Keq tells us which direction the reaction will proceed
If Q = Keq, the reaction is at equilibrium, conc=solubility and saturated solution
If Q < Keq then the reaction proceeds forward so Q gets closer to Keq, too many reactants conc Keq then the reaction proceeds in reverse direction (left) so Q gets closer to Keq, too many products conc>solubility *PRECIPITATE WILL FORM for Qsp > Ksp
Keq is only dependent on TEMPERATURE
When gases present can use partial pressure instead of concentrations to calc Keq
Categorize the following as kinetics or thermo: Activated complexes, reactants/products on free energy graph, delta G, intermediate, Ea
Activated complexes -> kinetics
Reactants/products on free energy graph -> thermo
delta G -> thermo intermediate -> thermo
Ea -> kinetics
Basically the 3 states (reactant, intemediate, and prod E) rep thermo and the hill size and transition states are kinetics
What is Ea? (like from where to where on free E graph)
What does the highest peak represent on the Free energy graph (in terms of kinetics)
Difference between reactant and highest energy transiton state (there could be more than one but one it taller than other)
The highest peak is the slowest step and known as the rate determining step
*Reaction rate equation
rate = -(1/r)(Δ[R]/Δt) = + (1/p)(Δ[P]/Δt) can see on equation sheet
r is coefficient
What changes Q? What changed K?
T, concentration, P, etc changes Q (Le Chat!!)
ONLY T changes K
*Changing volume of the Reaction Container
Changing the volume stresses an equilibrium ONLY if ______ of gas changes over the reaction
What happens if have
N2 (g) + 3H2 -> 2NH3(g) + heat
and the volume is decreased
A change in volume should cause a change in pressure (PV=nRT)
number of moles
Ex peep the coefficients of reactants and products and make sure coefficients of one side are larger on one than other
If the volume it decrease, this means the pressure increases and so we look back at equation and if the rxn shifts to the right, 4 moles of gas can be condensed into 2 moles, reducing the pressure to reestablish equilibrium
Changing temperature of the Reaction Mixture
You understand this so just read over
What happens when heat a rxn not at equilibrium?
Lowering temp favors the exothermic reaction, while raising the temperature favors the endothermic one
But when heat rxn when not at equilibrium, it gets to equilibrium faster and once it gets there, it will be affected by Le Chat
*Adding inert (or non-reactive) gas to a constant volume container vs constant pressure container
Constant volume container -> since inert gas does not participate in the reaction so it will change neither the partial pressure nor concentration of the products or reactants and since neither of these change then there is no change in equilibrium
Constant pressure container- (movable piston) If inject some helium in there, the volume will increase so pressure will decrease and this follow same rules as the changing volume pattern -> move to side with more moles
What does adding a catalyst do to equilibrium
Nothing bc equally increases rate of forward and backward reaction
Increases reaction rate but does not affect equilibrium
**Equation relating forward and reverse rates and Keq
Rforward = kf[A] Rreverse = kr[B]
At equilibrium Rforward = Rreverse
Kf[A] = kr[B]
*kf/kr = [B]/[A] = Keq
**Rate constant
Equilibrium constant
What happens to equilibrium constant if reverse equilibrium? What does combining multiple equilibria result in?
k
K
If reverse equilibrium, this inverts equilibrium constant (reciprocal so if it were
1 * 10^12, then it would be
1 * 10 ^ -12) I think this makes sense bc prod/reactants
Combining multiple equilibria results in multiplication of the equilibrium constants
*Compare Qsp vs Ksp to see if a _____ will form
If Qsp > Ksp then a precipitate will form if, for example, add another new compound to the solution
***Ca3(PO4)2 (s) -> 3Ca2+ + 2PO43-
How to see if precipitate forms?
Qsp = [Ca^2+]^3[PO43-]^2 = [5*10^-6]^3 [1*10^10]^2 = [125 * 10^-18] [1*10^-10] = 125 * 10^-28 1.25 * 10^-26 precipitate forms bc Qsp>Ksp
A salt’s solubility will ____ if it is added to a solution containing a common ion
A salt’s solubility will _____ if it is added to a solution containing something that removes a common ion (solubility effects in acid/base)
CaCO3(s) ->
A salt’s solubility will Decrease if it is added to a solution containing a common ion
A salt’s solubility will Increase if it is added to a solution containing something that removes a common ion
CaCO3(s) ->
*For a reaction AB -> A + B, what does the Kd and Ka equation look like, how does it relate concentrations and forward vs reverse rates?
K2/K1 = [A][B]/[AB] = Kd
K2 is rate constant for forward reaction, K1 is rate constant for reverse rxn
K1/K2= [AB]/[A][B] = Kaff
Kaff = 1/Kd
Words mxn, transition state are associated with thermo or kinetics?
Kinetics
What kind of reactions are neutralizations (endo or exothermic)?
Neutralizations are exothermic
*Chemical equilibrium
the concentrations of the products and reactions are static
Chemical equilibrium
the concentrations of the products and reactions are static
INCORRECT: the rate constants of the forward and reverse reactions are equal.
