CHEM 112 - MIDTERM II Flashcards
Reaction with a faster rate will have more _____.
products formed
Rate expression
rate = -1/a [A]/ t = -1/b [B]/ t =- 1/c [C]/ t
Average rate vs. instantaneous rates
Average rate: rate of the reaction over a certain period of time (takes the two time points from initial to final to find the change in concentration)
Instantaneous rate: rate of the reaction at a given time (ie. t = 2 s)
The rate of the reaction is ____ to the concentration of the reactants
proportional
The rate constant depends on ____ & ____.
Temperature & reaction specific properties
rate law
rate = k [A]^ x [B]^y
where x & y are integers that give the order of the reaction w/ respect to each reactant
Zero order
No dependence on the concentration ([A]0 = 1); change in concentration does not equal change in rate
First order
The rate of the reaction is directly proportional to the reactant concentration ([A]^1 = [A])
Second order
The rate of the reaction is directly proportional to the square of the reactant concentration ([A]^2 = [A]^2)
Integrated rate law
Describes the relationship between the concentrations of the reactants and time (depends on the order of the reaction)
Zero order Integrated Rate Law
[At] = -kt + [A]0
First order IR Law
ln [A]t/[A]0 = -kt
Second order IR Law
1/[A]t = kt + 1/[A]0
Slope for zero order IR
-k
Slope for first order IR
-k
Slope for second order IR
+k
Half-life
Time required for the concentration of a reactant to fall to 1/2 of its initial value
Find half-life on graph
see y-intercept and divide by 1/2 - the x-intercept (time) = half life
Zero order half life
t 1/2 = 1/k x [A]0/2
First order half life
t 1/2 = 1/k * 0.693
Second order half life
t 1/2 = 1/k x 1/[A]0
Factors that affect reaction rates
1) Concentrations
2) Temperature
3) Catalysts
Catalysts ____ the activation energy by providing a ____ energy path from reactants to products
lower; alternate, lower energy path
Arrhenius Equation
Relates the rate constant (k) and the temperature in kelvins
k = A x e^ -Ea/RT
The exponential factor of the Arrhenius equation ____ with increase in temperature
increases
The exponential factor of the Arrhenius equation ____ with an increase in activation energy
decreases
The higher the Ea, the _____ the reaction rate at a given temperature
slower
Hrxn < 0, the reaction is ___
exothermic
Hrxn > 0, the reaction is ___
endothermic
Increase in temp in the Arrhenius equation also results in ___
increase in rate constant (k)
The frequency factor in the Arrhenius equation (A) is smaller when ____
the molecules do no not collide in the right way, resulting in a slower rate
How would the rate of a reaction change if a catalyst was added (decreasing activation energy) and everything else was the same?
Reaction rate increases
How would the rate of a reaction change if a catalyst was added (decreasing activation energy) and everything else was the same?
Reaction rate increases
Elementary step
Process that occurs in a single step
In multi-step reactions, the elementary steps ___
must add up to give overall equation
Two reactant molecules participate in each step, so they are both _____
bimolecular
Each ___ on the graph is associated with the _____.
peak; activation energy
The number of valleys on the graph is equal to ______ the number of steps in the mechanism
one less than
2 valleys = ___ reaction steps
3
The barrier with the ____ activation energy is the _____.
largest; rate-determining step
The number of peaks tells you the ______.
number of transition states
The difference in the energy of the products and reactions tells us whether the reaction ____ or ___ energy
emits; absorbs
Slow step = ____
higher activation energy
Reaction mechanism must have these two conditions met:
1) elementary steps in the mechanism must sum to the overall reaction
2) rate law predicted by the mechanism must be consistent with observed rate law
Catalyst
Changes the speed of a chemical reaction without undergoing a permanent chemical change itself
Catalyzed vs. Uncatalyzed graphically
catalyzed (lower Ea)
If you multiply a reaction by a certain number (n), ____ the original Kc you multiplied by (n).
raise the original Kc to the n power
If you add two reactions together, ____ the two K together to get the new K.
multiply
When the equation for the reversible rxn is written in the opposite direction, the new Kc becomes ____.
a reciprocal (1/Kc)
K > 1 @ equilibrium, then ___
[products] > [reactants]
K is very large (10^10), then ___
reaction goes to completion (favors forward rxn)
K is very large (10^-10), then ___
reaction does not occur (no product is formed)
Kp & Kc relationship?
Kp = Kc (RT)^n
where n = products - reactant coefficients [consider stoichiometry]
If Q= K ____
rxn is at equilibrium
Q>K, ____
rxn needs to shift to the left (towards reactants) to reach equilibrium
Q<K, _____
rxn will shift to the right (towards products) to reach equilibrium
Le Chatelier’s Principle
A change in any of the factors that determine the equilibrium will cause the system to adapt in that manner to reduce the effect of change
What triggers Le Chatelier’s Principle?
1) Adding/Removing a reactant or product
2) Changing the temp
3) Changing the volume (or pressure) of the reaction vessel
For rxns with unequal moles of gases in the reactants and products, ______ will cause a shift to the side with less moles of gas
decrease in volume
Increase in product causes the rxn to ____
shift left (towards reactants) to re-establish equilibrium
Increase in pressure causes the rxn to ___
Reaction will shift toward the side with fewer moles of gas particles
Decrease in pressure causes the rxn to ___
Reaction will shift toward the side of the rxn with more gas particles
If the moles were equal on both sides of the reaction then the change in pressure ______.
will have no effect!!!
Increase in temperature as a reactant highlights a _____ reaction, in which the rxn will shift to the _____.
endothermic (heat is reactant); right
Decrease in temperature as a reactant highlights a _____ reaction, in which the rxn will shift to the _____.
exothermic; left (produces heat)
Increase in temperature as a product highlights a _____ reaction, in which the rxn will shift to the _____.
exothermic (heat is product) ; left
Arrhenius acid
Substance that contains H and produces H+ in solution
Example of Arrhenius acid
HCl
Arrhenius Base
Substance that contains OH and produces OH- in solution
Example of Arrhenius Base
NaOH
Bronsted-Lowry Acid
Species that donates a H+ in a chemical reaction
Bronsted-Lowry Base
Species that accepts H+ in a chemical reaction
Bronsted-Lowry Acid in HCl + H2O -> Cl- + H3O+
HCl
Example of Bronsted-Lowry Base
NH3 + H2O
HA in this equation is the ____
HA + H2O -> A- + H3O+
Bronsted-Lowry Acid
OH- in this equation is the _____
OH- + H2O -:> H2O + OH-
Bronsted-Lowry Base
A- in this equation is the ____
A- + H2O -> HA + OH-
Bronsted-Lowry Base
Water is a Bronsted-Lowry ____
acid & base
Water is a Bronsted-Lowry ____
acid & base
Every Bronsted-Lowry acid has a _____
conjugate base
Conjugate base
Always has one fewer H atom and one more negative charge than the formula of the corresponding acid
Conjugate base to CH3COOH is ____
CH3COO-
Conjugate base to NH4+ is ____
NH3
Conjugate base to HCl is ____
Cl-
Conjugate base to H3O+ is ____
H2O
Conjugate base to H2O is ____
OH-
Conjugate acid to CN- is ____
HCN
Strong aid ______ in water
completely ionizes (single arrow rxn)
Weak acid _____ in water
partially ionizes (reversible)
HF is a ______ acid
weak
Acetic acid is a _____ acid
weak
Strong base _____ in water
completely disassociates
Weak base _____ in water
partially disassociates
Ammonia (NH3) is a _____ base
weak base
Ammonia (NH3) is a _____ base
weak base
Hydroiodic acid is a _____ acid
strong (HI)
Perchloric acid is a ____ acid
strong (HClO4)
Hydrobromic acid is ____ acid
strong (HBr)
Hydrochloric acid is ___ acid
strong (HCl)
Sulfuric acid is ____ acid
strong (H2SO4)
Nitric acid is a _____
strong (HNO3)
Three strong bases
1) NaOH
2) KOH
3) Ba(OH)2
The stronger the acid, the _____ its conjugate base
weaker
The stronger the base, the _____ its conjugate acid
weaker
HI + H2O –> _____
H3O+ + I-
F- + H2O –> ____
HF + OH-
Water is a _____ electrolyte
weak
H2O –> ____
H+ + OH-
Autoionization of water is ____
Kw
Kw = _____
Kw = [H+] [OH-]
Kw @ 25 degrees C ______
1 x 10^-14
In pure water [H+] = ______ and [OH-] = ______ respectively
1 x 10^-7 M
pH formula
pH = -log (H+)
Finding H+ concentration with pH
[H+] = 10^-pH
pOH formula
pOH = -log (OH-)
Finding OH- concentration with pOH
[OH-] = 10^-pOH
Finding pH with pOH
pH + pOH = 14
[H+] > [OH-] means the pH is _____
acidic (less than 7)
Weak acids utilize the ______
Acid dissociation constant (Ka)
Strong acids do not have a _____ value
Ka (because they fully dissociate)
We can calculate the pH of a weak acid by ___
Using an ice table, writing the equilibrium constant expression, solving for x to calculate equilibrium concentrations for all species, and using the equilibrium concentration of H+ or OH- to determine pH
We can use the small x approximation, if the Ka given is _____
x 10^-6 or less & the concentration is fairly high >0.05 M
this removes the need to do the quadratic formula by leaving the initial concentration as is
Polyprotic Acids
Acids that have more than one ionizable H atom; each successive H+ is harder to remove
The pH of the polyprotic acid depends only on the ____
first proton (Ka1)
The bigger the Ka value, the ___ the weak acid
stronger
Small Ka value = _____
weaker weak acid
How can salt solutions impact pH?
Salt (ionic compound) fully ionizes in a solution
If ionic product s is the conjugate acid of a weak base it will _____.
It will react with water to produce the weak base and hydronium ions
The weak base (A-) produced will react with water to produce the ____ and hydroxide ions
conjugate acid (HA)
If both weak acid and weak base are present in the solution, how can we predict the pH?
Compare Ka & Kb values and the larger value will dominate the equilibrium
small Ka & large Kb = solution is basic
Find Ka or Kb with which formula?
Kw = Ka x Kb
Strong acid and strong base cations and anions (NaCl & KI) will result in pH _____
pH = 7; no impact on the solution
How do we solve: Which of these salt solution will be most acidic?
Compare Ka and Kb values; whatever value has the highest Ka value is the most acidic
