GChem: Kinetics & Equilibrium (GOOD review) Flashcards

1
Q

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?

A

Intermediate -> Molecule generated then consumed
Catalyst -> Consumed then regenerated, conc doesn’t really change
Transition states not shown

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2
Q

How to determine what the rate determining steps is:

What 3 factors determine a fast rate?

A

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

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3
Q

Activated complex

A

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

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4
Q

Label reaction coordinate diagram

What do the peaks rep? what does the hole in middle rep? Where is Ea? Where is delta G?

A

pg. 187

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5
Q

Does ΔG thermo or kinetics?

MCAT LOVES TO MIX THESE TWO TO TRICK YOU

A

THERMO!

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6
Q

How to determine is something is a catalyst by looking at rxn steps

A

The catalysts is consumed but reformed at the end of the rxn

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7
Q

Does catalyst affect ΔG, ΔH, ΔS?

A

Catalyst does NOT affect ΔG, ΔH, ΔS bc catalyst is kinetics but ΔG, ΔH, ΔS is thermo!

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8
Q

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?

A

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

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9
Q

*How to determine orders of reactants based on experiment?

How do we get rate constant?

A

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

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10
Q

*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

A

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

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11
Q

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 ___

A

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

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12
Q

What factor affects both kinetics and thermodynamics?

A

Temperature

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13
Q

What can you have a solution of?

A

Anything

ex. 2 gases

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14
Q

Like dissolves like

A

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

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15
Q

Why is electrolyte called an electrolyte?

A

Bc due to the free ions, the solution can conduct electricity

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16
Q

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?

A

Bc due to the free ions, the solution can conduct electricity
i = 1
Ionic compounds are the best type of electrolytes

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17
Q

Which of the following is the weakest electrolyte

a) NH4I
b) LiF
c) AgBr
d) H2O2

A

H2O2 is covalent compound

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18
Q

Dynamic equilibrium
Chemical equilibrium

Where are we in the process when we have reached molar solubility?

A

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

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19
Q

Online: What is difference between molarity and concentration?

A

Molarity -> moles solute/ Liters solution (volume)

Concentration -> grams/Liter

20
Q

**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?
A
  1. The solubility of solids in liquids tends to increase with increasing temp (sugar in hot tea)
  2. The solubility of gases in liquids tends to decrease with increasing temperature (warm coke)
  3. The solubility of gases in liquids tends to increase with increasing pressure
21
Q

**ON MCAT

Salt Solubility Rules (3)

A

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

22
Q

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?

A

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

23
Q

What does sp mean? What do these values PHYSICALLY MEAN?

When Qsp > Ksp
When Qsp = Ksp
When Qsp < Ksp

A

When Qsp soluton saturated

When Qsp>Ksp -> excess salt will precipitate

24
Q

Common ion effect

A

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

25
**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
26
**What factors can change K?
ONLY temperature
27
**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
28
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
29
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
30
*Reaction rate equation
rate = -(1/r)(Δ[R]/Δt) = + (1/p)(Δ[P]/Δt) can see on equation sheet r is coefficient
31
What changes Q? What changed K?
T, concentration, P, etc changes Q (Le Chat!!) | ONLY T changes K
32
*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
33
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
34
*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
35
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
36
****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
37
**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
38
*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
39
***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 ```
40
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) ->
41
*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
42
Words mxn, transition state are associated with thermo or kinetics?
Kinetics
43
What kind of reactions are neutralizations (endo or exothermic)?
Neutralizations are exothermic
44
*Chemical equilibrium
the concentrations of the products and reactions are static
45
Chemical equilibrium
the concentrations of the products and reactions are static | INCORRECT: the rate constants of the forward and reverse reactions are equal.