Exam 2- Equilibrium, Acids and Bases Flashcards
Reaction Quotient
Qc, ratio of [product]/[reactant], raised to its stoichiometric coefficient.
Used when a reaction is NOT at equilibrium
Equilibrium Constant
Keq, ratio of [product]/[reactant] raised to its stoichiometric coefficient WHEN AT EQUILIBRIUM
Dynamic Equilibrium
A state in which forward and reverse processes are occurring at the same rate, resulting in no observable change in the system. Continual reaction going in both directions
Equilibrium
When the forward rate matches the reverse rate. Appears as those it has stopped but in actuality forward matches reverse.
What does it mean when the Keq is greater than 1?
The reaction goes to completion; favor products, spontaneous as written
What does it mean when the Keq is less than 1?
The reaction doesn’t occur; favor reactants, nonspontaneous as written
Can Keq equal zero when in equilibrium?
No. Always a product, always a reactant.
Do all reactions exist in equilibrium?
No. Ex: burning paper. We cannot change this outcome, cannot control forward/backward by any manipulation.
Keq and Concentration Vs Time Graph
LeChatelier Principle definition
When a stress is applied to a system at equilibrium the system will respond by shifting in the direction that minimizes the effect of the stress
LeChatelier’s Principles
When _______ a _______, in order to maintain the equilibrium constant, the reaction must shift to ________ and __________
When adding a reactant, the reaction must shift to products and produce more product.
When adding a product, the reaction must shift to reactants and produce more reactant
When removing a reactant, the reaction must shift to reactants and replace the removed reactant
When removing a product, the reaction must shift to products and replace the removed product.
Why does LeChatelier’s Principle make sense?
Collision theory. Increase (or decreasing) concentrations will change number of collisions, changing the rate, which changes the equilibrium.
Ex: adding a reactant increases collisions, which increases products, which increases the reverse process to make reactant….this is equilibrium :)
Which states are not used in determining Keq, and why?
Solids and Liquids are not included in Keq expressions because their amount is so very large it would make minimal impact on the Keq.
Write the equilibrium constant expression for 2N2O= 4NO2 + O2
. [NO2]^4 [O2]
Keq= ——————–
[N2O]^2
List different types of Keq’s and when to use them
Kc- equilibrium constant expressed in terms of concentration (molarity)
Kp- Equilibrium constant expressed in terms of pressure (atm, mmHg)
Ka- Acid dissociation constant
Kb- base dissociation constant
Ksp- Solubility product for compounds that do not dissolve well
Kf- Formation constant for large Keqs
Kd- Dissociation constant
Equation for converting Kc to Kp (is on equation sheet but delta n is not, know your R)
Kp=Kc(RT)^n
delta n is found by SUM of Coefficient products - SUM of Coefficient reactants
Recall R is not gas constant, its pressure constant - 0.0821 amt L/M K
How do we know when we are at equilibrium?
When the ratio of products to reactants equals the accepted equilibrium constant.
Any other condition of ratios results in reaction quotient (Q)- not at equi
How can reaction quotient tell us the direction of a reaction?
When Q>Keq, more products or less reactants that we would find at equi. Therefore reaction shifts left
When Q<Keq, less product or more reactant than we would find at equi. Reaction shifts right
if Q=Keq means we are at equilibrium
Things to remember when finding Keq
1) Know what we K is being asked to find (pressure, concentration, acid, base…)
2) if concentration, be sure to find molarity: M=moles/Liters.
If asked to convert Kc to Kp:
3) Find delta N (coeff produc-coeff react)
4) R is not gas constant, its pressure constant
5) Temp in K
What is an ICE table?
Initial Concentration
Change
Equilibrium Constant (Keq)
If given any one of these, we can solve for the missing
What should you watch out for when an equation consists of only gases?
Kp or Kc. Must know which one the question is asking for an be able to convert.
What is delta n, how is it calculated and what is it for?
Delta N is used in the conversion of Kc to Kp.
moles of products-moles of reactants
When is the only time Kp=Kc?
When N=0; moles of products equal the number of moles of reactant (because when plugged into the conversion equation, anything to the zero power is 1)
A reaction with a very large K( much greater than 1) will have what Gibbs sign?
Negative delta G. Reactions will combine spontaneously to form products. Equilibrium mixture will consist mostly of products
A reaction with a very small K (must less than 1), will have what Gibbs sign?
Positive delta G. Will not combine spontaneously to form products, meaning equilibrium mixture will consists mostly of reactants.
K>Q
Ratio is too small, To reach equilibrium reactants must be converted to products. System proceeds forward(left to right)
G is negative
Q=K
Equilibrium concentrations. no change
G=0
K<Q
Ratio is too large, to reach equilibrium products must be converted to reactants. System proceeds in reverse (right to left)
G is positive
The larger K is the ________ G^o will be
The larger K is, THE MORE NEGATIVE G^o will be.
Important difference between ΔG and ΔG°
It is the sign of ΔG and not that of ΔG°
that determines the direction of reaction spontaneity.
The sign of ΔG°
only tells us the relative amounts of products and reactants when equilibrium is reached, not the direction the reaction must go to reach equilibrium.
Relationship between K, ln K, and G
When changing concentrations, if you increase the denominator, what happens to your final value?
It will decrease.
Q= prod/react.
by increasing reactants, we will decrease Q, K remains the same but if Q changes we are no longer at equilibrium. Once reaction shifts the ratio will return to K
What happens to pressure when you decrease the volume of a container?
How does a reaction shift to compensate for this change?
The pressure will increase
The reaction will shift towards the side with less moles.
Ex: CO + 2H = CHOH
1 + 2=3 1 Products have less, so shift will go to the right, toward products.
What happens to a reaction when you decrease the temperature?
Must know the H to determine endo vs exo in the forward reaction. Decreasing heat will shift toward the exo reaction.
According to LeChateliers Principle, If you increase the concentration of a product, which way will it shift?
A + B = C + D
increase concentration of products ( C or D) reaction will shift left towards reactants to balance out the new [ ].
If you increase the concentration of a solid or liquid, how does that effect the equilibrium reaction shift?
Solids and Liquids do not effect K (equilibrium) therefore it will not shift.
How does a catalyst change the equilibrium shift?
It doesn’t. It will speed up the reactants to products rate, which will also speed up the products to reactants, but will not change the concentration so no effect on position of equilibrium
When can Kc and Kp be equal?
ONLY when the reaction results in no net change in the number of moles of gas (when n=0, because anything to 0 power is 1)
A negative delta G corresponds to a ____ K, and a positive delta G corresponds to a ___K
A negative delta G corresponds to a __large__ K,
and a positive delta G corresponds to a _small__K
What are the only stresses that can be added to a reaction that will change the equilibrium, according to LeChatelier
Add or remove a substance, change in volume (which will change pressure), and change in temperature
Law of Mass Action
For a reversible reaction at equilibrium and a constant temperature, the reaction quotient, Q, has a constant value, K
Bronsted Acid vs Bronsted Base
Acids donate a proton, bases will accept a proton
Conjugate Acids vs Conjugate Bases
When a Bronsted acid donates a proton, what is left is the conjugate base.
What are the conjugate pairs for
HCl + H2O = H3O+ + Cl-
HCl acid and Cl conj base
H20 base and H3O conj acid
Which type of acids and bases (weak or strong) reach equilibrium easily and which have a harder time reaching equilibrium? Why?
Strong acids and bases have a hard time reaching equilibrium because they fully dissociate. 1 mole of reactant will dissociate into 2 total moles (1+ and 1- ion).
Weak acids and bases dissociate into a fraction and reach equilibrium more easily.
List of Strong Acids and Bases
Acids: HCl, HBr, HI, HNO3, HClO4, H2SO4
Bases: LiOH, NaOH, KOH, RbOH, Sr(OH)2, Ba(OH)2
Strong acids and bases are _____electrolytes
Strong acids and bases are STRONG electrolytes
What is a strong electrolyte
Means it will disassociate completely in solution, it will conduct electricity very well.
What is the definition of an Arrhenius acid and base?
Acid: any compound that donates and H+ ion to water
Base: any compound that donates an OH- to solution
Bronsted-Lowry definition of Acid and Base
Why do we care?
Acid- any substance that donates a an H+ ion (independent of water, works under any circumstance)
Base- Any substance that accepts an H+ ion (does not involve OH- and does not include water)
Important BL take way: Bronsted-Lowry track where H+ ions are going within a chemical reaction. When this happens in water, we can track it by measuring the pH of the solution.
Lewis acid and base definitions
Acid- Any compound that accepts a lone pair of electrons
Base- any compound that donates a lone pair of electrons
Keep going!
Because you are the best and I love you!
In short, what are the different focuses between Arrhenius, Bronsted-Lowry, and Lewis acid/bases?
Arrhenius- OH and H, in water
B/L- Just H regardless of solute
Lewis- track lone pairs
What is pH
Gives us a format to compare acids and bases.
By definition, pH is
-log[H+]
Typically 1(acidic) -14 (basic)
7 is neutral ( H+ = OH- )
Define amphoteric
give an example
molecules that can act as both acid and base- according to Bronsted-Lowery theory
Rule of 100
C/K > 100 you can ignore the x for that concentration only.
Explain why Dynamic Equilibrium exists
(likely a short answer exam question)
Collision theory: If you increase the concentration of Reactant it will increase the number of successful collisions, which will increase the forward rate, which increases the concentration of product, which increased collisions, which increases the reverse rate, which as some point will equal the forward rate, and appear like the reaction is at a standstill, but really the forward and reverse rates match.
Is water a weak or strong electrolyte?
Weak-not on list of strongs, but can still conduct some electricity.
Equilibrium expression for the autoionization of water, and the equation
H2O(l)+H2O(l)=H3O+(aq)+OH-(aq)
Kw= [H3O+] [OH-]
or
Kw= [H+] [OH-]
Hydronium Ion
H3O+, water with an extra H+ ion.
A large Ka (usually great than one) means a _____acid, while a small Ka (less than one) means a ____acid.
Ka> 1 = strong acid, will dissociate easier
Ka<1 = weak acid
What does Ka tell us?
How attached the H+ is to the molecule and the overall structure
The higher the Ka, the easier to dissociate, stronger acid
What does Kb tell us?
Kb looks at the amount of OH- on the product side of the equilibrium. It focuses on the ability of the substance to extract an H+ from water.
Based on molecular structure, arrange the following sets of oxyacids in order of increasing acid strength.
HClO3 , HIO3, HBrO3
What about diatomic acids HCl and HI
All belong to the same group
As one goes down the group, the atomic size increases and electronegativity decreases. Electronegativity is the ability of an atom to pull electrons towards itself. This is the trend for Oxyacids only! Diatomic acids like HCl vs HI are the reverse, HI>HCl
HIO3 < HBrO3 < HClO3
Which is the stronger acid?
H2SO4 or H2SO3
HNO3 or HNO2
HClO4 or HClO3 or HClO2
The more O the stronger the acid, because of oxidation state. Stronger acid=larger Ka=easier to lose H
H2SO4>H2SO3
HNO3 > HNO2
HClO4 > HClO3 > HClO2
A large Kb means that the stubstance is very ______at taking an H+ from water.
A small Kb means the substance is ___ at taking an H+ from water
A large Kb means that the substance is very good at taking an H+ from water. Likewise a small Kb means the substance is not very good.
When NaCl is dissolved in water there is no pH change. Why?
if NaC2H3O2 were dissolved in water pH would change. Why?
NaCl is a 1:1 and fully dissociates. [H+]=[OH]
NaC2H3O2 will alter the pH since it will not fully dissociate [H]<[OH] (recall Na is a spectator in this ionic bond, while C2H3O2 will bond with H2O and transfer H)
[H+]>[OH-] then pH drops below 7.
[H+]<[OH-] then pH rises above 7.
Must determine if the ions extract H or OH by forming weak acids or bases?
Define Polyprotic Acid
Acids that contain more than one H+. These will dissociate in steps, never all at once. Each step with its own Ka.
In polyprotic acids , which Ka should be the greatest. Why
the first Ka should be the greatest. It is easier to remove a proton from a neutral species than one with a neg charge. Smaller charged species are easier to remove a proton from than larger charged species.
Large K value means _______acid/base, means _____ to lose a H+
A larger K value means a stronger acid/base, means easier to lose an H+ because strong acid/base dissociate completely, losing their H+
The Larger the K value, the ______ the acid
The larger the K value the stronger the acid. The stronger the acid the easier it will lose an H+
Ka Vs Kb
Ka- watching the H+ leave the acid. Higher Ka means its losing its electrons to the central atom (because of electronegativity) so H will leave to get new electrons.
Kb- readily accepts the H+. Higher Kb means more readily accepts it, means more products can be formed.
Larger K values (whethr ka, kb, or kc…) have ______ products
Larger K values have more products than those of smaller K values
