Chem 112B Final Flashcards
Collision theory
The rate of a chemical reaction is proportional to the number of collisions between reactant molecules.
The more often reactant molecules collide, the more often they react with one another, and the faster the reaction rate
In a reaction profile, peaks are… and valleys are…
transition states, intermediate states
Reaction energy (ΔE) is
the energy of products minus the energy of the rectants
Activation energy (Ea) is
the energy needed to get to the peak, can be either TS-reactant or TS-intermediate
In an elementary reaction, the method of initial rates
Rate = k[A]^x{B}^y
x and y are the same as a and b
In a multi-step reaction, the exponents
must be determined experimentally
Reaction mechanism consists of
elementary steps
Rate law is always based on the
slowest step
How do I know if a reaction is elementary or not?
All reaction steps in a reaction mechanism are elementary
If the first step is the fast step, will it always be an equilibrium reaction?
Yes. For fast first step, use equilibrium to solve for concentration of intermediate
1st order integrated rate law
plotting ln[A] vs time gives a straight line. Half-life only depends on k
2nd order integrated rate law
plotting 1/[A] vs time gives a straight line. Half life depends on both k and [A]0.
Plotting lnk vs 1/T gives a
straight line
slope = -Ea/R
y-intercept = lnA
At two different temperatures, we can determine Ea or ratio of k using which two equations
lnk = -Ea/RT + lnA
lnk1/k2 = Ea/R [1/T2 - 1/T1]
At a fixed temp, we can use difference in Ea to determine..
ratio of k
kcat/kuncat= e (,..)
H-bond donor
strongly electronegative atom such as N, O, or F
H-bond acceptor
electronegative atom of a neighboring molecule or ion that contains a lone pair
To be phosphorylated, a side chain must
contain alcohol or amine group
if the half-life is constant, the order is
1st order
Intermediate
Produced, then consumed
Catalyst
Consumed, then produced
Rate of forward process=
Rate of reverse process
For elementary reactions, Keq=
kf/kr, where kf are rate constants for the forward and reverse reaction, respectively
K»_space; 1
Products predominate
K «_space;1
Reactants predominate
Keq for the reverse reaction is the
inverse of Keq for the forward reaction
When a reaction has been multiplied by a number, Keq for the new reaction is the
original Keq raised to a power of the multiplication factor
If the net reaction can be obtained by the addition of 2 or more steps, Keq is the
product of the individual Keq
Q
reaction quotient
Q is calculated using…Keq is calculated using…
Any concentrations, equilibrium concentrations
Q< Keq
Reaction shifts right (produce more products, consume more reactants)
Q > Keq
Reaction shifts left (produce more reactants, consume more products)
At equilibrium, added reactants or products will cause the reaction to shift to
consume towards to reestablish equilibrium (balance scale)
Add reactants or remove products
Reaction shifts right
Remove reactants or add products
Reaction shifts left
Since pressure is increased by disturbance, reaction will shift in direction that
reduces pressure
Decreasing the volume shifts the reaction to the side with
less moles of gas
If a reaction has the same moles of gas on both sides, changing pressure/volume does
NOT have any effect on equilibrium
When heat is added to a system at equilibrium, reaction shifts in the direction that
absorbs heat
Spontaneity
process proceeds in forward direction to an appreciable extent by itself
Free energy of formation at standard conditions can be calculated using
ΔG°f = ΔH°f - (298K)ΔS°
Calculate ΔG° at 25°
ΔG° = ΔH° - (298K)ΔS°
Calculate ΔG° at temps besides 25°
ΔG° = ΔH° - TΔS°
ΔG° = -RTlnK
ΔG > 0, Q > K
System is nonspontaneous in forward direction
ΔG < 0, Q < K
System is spontaneous in forward direction (system does work)
Endothermic ΔH
positive
Exothermic ΔH
negative
Molar entropy increases when
Gaseous, largest molar mass, most molecular complexity, volume increases, pressure decreases
Increased Kd means
Weaker binding
Decrease in entropy of a reaction
Decrease is numbers of gaseous or aqueous molecules
Increase in entropy of a reaction
Solids dissolve
Endothermic (s->l->g)
Volume increase
7 strong acids
HClO4, HI, HBr, HCl, H2SO4, HNO3, HClO3
8 strong bases
KOH, LiOH, NaOH, Ca(OH)2, Ba(OH)2, RbOH, Sr(OH)2, CsOH
Group 1A and heavy group 2A hydroxides are
strong bases
Amines are
weak bases
Carboxylic acids and thiols are
weak acids
The conjugate base of a strong acid is
a negligible base
The conjugate base of a weak acid is a
weak base
For weak acids and bases, the stronger the acid, the
weaker its conjugate base
Within the same group,
larger atoms means stronger acid
Within the same period, higher electronegativity means
stronger acids
The more electrognegative the central atom, he higher the
number of oxygen atoms attached, the stronger the acid
Non-metal oxides/hydroxides are
acidic
For pure water,
[OH] = [H]
Strong acids and strong bases are strong electrolytes, so they
dissociate completely in water
Larger Ka, smaller pKa
Stronger acid
Smaller Kb, larger pKb
Weak base
Addition of a common ion decreases
ionization
Buffer
solution that contains a weak acid and salt of its conjugate base
solution that contains a weak base and salt of its conjugate acid
To make/produce buffer
Combine weak acid and salt of conjugate base/ vice versa
OR use neutralization to combine excess weak acid with a strong base
Optimal pH of a buffer =
pKa
More concentrated buffer solution has
greater capacity
Equivalence point is when
stoichiometrically equivalent quantities of acid and bASE REACTED
At half eq point, pH=
pKa
Solubility
Maximum amount of solid that will dissolve under a given condition, forms a saturated solution
If Q > Ksp
precipitate will form
If Q < Ksp
More solid can be dissolved
Chelating ligands have
two or more donor atoms
Larger Kf (more stable) is mostly due to the
entropy effect
Electrode of a voltaic cell
GRedCat, LAnOx
Salt bridge of voltaic cell
to neutralize excess charges (anions to anode, cations to cathode)
External circuit of a voltaic cell
e- flow from anode to cathode
Oxidizing agent
Gains e-, gets reduced
Reduction agent
Loses e-, gets oxidized
The more positive E°red
the more spontaneous and one will undergo reaction (at cathode)
Determine which electrode is cathode and anode
- Write reduction half rxns,
- Compare E° red , the more positive (spontaneous) one will undergo reduction (at cathode)
Calculate standard cell potential
- Write oxidation and reduction half rxns,
- E° cell = E° ox + E° red
Connect free energy (and work) to cell potential
- ∆G = –nFEcell and ∆G o = –nFE°cell
- Ecell is (+), ∆G is (–), rxn/process is spontaneous
Describe electrolysis and electrolytic cell (Drive nonspontaneous rxns by
applying electrical energy.)
- Consist electrodes in either aqueous solutions or molten salts.
- Oxidation still at anode, reduction still at cathode.
- Be able to differentiate voltaic cell and electrolytic cell.
Predict products at cathode or anode of electrolytic cell
- Identify all species in solution
- Write half reactions with species as reactants
- Compare potentials to predict products
Do quantitative calculations involving electrolysis
- Write balanced half reactions
- Use datasheet conversions for amps, volts, Faradays, etc.
Linear combinations of wavefunctions to create molecular orbitals
- Same number of MOs created: bonding and antibonding
- Each MO holds maximum of 2 electrons
Bonding orbitals (lower energy)
- Sigma (σ) : e density on axis
- Pi (π): e density above and below
- Subscript of original AO
Anti-bonding orbitals (higher energy):
- Node between nuclei
- Star superscript
Fill MOs of diatomic molecules/ions:
- Fill lower MOs first.
- For degenerate MOs, singly occupy first before doubly up.
Predict bond order using MO diagram:
- BO = ½(#BE - #AE)
- Bond order of zero means substance is very unstable (does not exist)
Coordination compound is a
neutral compound of the metal complex ion + counter
ion(s)
Inside the bracket of the coordination compound is the
metal complex (ion),
which has a transition metal cation + ligands covalently bond (coordinated) to it.
Outside the bracket is the
counter ion(s)
The charge of the metal complex =
– (total charge of counter ions)
In water, coordination compound fully dissociates into
the metal complex and counter ions
The coordination number of the metal is
the number of donor atoms (from the ligand) that are bonded/coordinated to the metal cation
Describe metal complex
- Transition metal act as Lewis acids (accept e – pair);
- Ligands act as Lewis bases (donate e – pair)
Crystal field theory
Δ = Crystal field splitting energy
Large Δ ->Strong Field -> Low spin
Small Δ -> Weak Field -> High spin
Paramagnetic
have unpaired electrons
Diaamagnetic
No unpaired electrons
Units of 0 order
Ms^-1
Units of 1st order
s^-1
Units of 2nd order
M^-1s^-1
4 factors that affect reaction rates
Inc contact area = faster
Inc concentration = faster
Inc temp = faster
Catalyst lowers Ea = rate faster
Small Km,
strong binding
Inc kCat, small Km,
Efficient enzyme
Q < Keq
Reaction proceeds reverse, more reactant produced
Q > Keq
Reaction proceeds forward, more product produced
Endothermic heat is the
reactantE
Exothermic heat is the
product
Kb =
Kon/Koff
Kd =
Koff/Kon
Large Koff=
weak binding
Large Kb=
Strong binding
Small Kd =
Strong binding
nm to um
divide by 1000
Ki =
Koff/Kon
Competitive inhibition
Vmax not affected
Km increases
Noncompetitive inhibition
Vmax decreases
Km stays same
Fewer H-bonds raises
Ki
Weaker interactions, Ki
increases
For a process to be spontaneous, ΔS must be
+
When ΔH and ΔS is negative,
ΔG is negative at low T (spontaneous)
ΔG is positive at high T (nonspontaneous)
When ΔH and ΔS is positive,
ΔG is negative at high T (spontaneous)
ΔG is positive at low T (nonspontaneous)
When ΔH is negative and ΔS is positive,
ΔG is negative (spontaneous)
When ΔH is positive and ΔS is negative,
ΔG is positive (nonspontaneous)
Arrhenius acids produce
H+ when dissolved in water
Arrhenius bases produce
OH- when dissolved in water
Bronsted acids
donate H+
Bronsted bases
accept H+
Ka increases
acidity increases
Stability of conjugate base factors
larger atom
electronegative
resonance
inductive effect (electronegativity)
Lewis acids
accept e- (incomplete octets)
Lewis bases
donate e- (at least 1 lone pair)
Ligand is the molecule or ion that
bonds to a metal or ion
Coordination number
The number of atoms bonded to the metal (# of bonds metal forms)
Acidic
H > OH
Basic
H < OH
Cation
positive charge
Anion
negative charge
