Chapter 15-17 test Flashcards
What is dynamic equilibrium?
When the rate of a forward reaction = the rate of a reverse reaction. When this happens, it appears that the reaction is complete because the amounts of reactants and products are no longer changing.
- Dependent on temp.
- Does not mean equal amounts of reactants and products
- Achieved from either direction
What is Keq?
- The equilibrium constant
- Because the concentration of reactants and products are no longer changing, their proportion will be constant and is a helpful quantitative measure to describe an equilibrium position.
- Only aqueous and gas species, no solids or liquids
- Dependent on temp.
Keq = [products]^x/[reactants]^y
What does it mean when Keq is greater than 1?
The products predominate and the equilibrium lies to the right (more products at eq.)
What does it mean when Keq is less than 1?
The reactants predominate and the equilibrium lies to the left (more reactants at eq.)
What does it mean when Keq is equal to 1?
There are equal amounts of reactants and products
What is Kc?
Keq in terms of concentration
What is Kp?
Keq in terms of pressure
What happens to the Keq when a reaction is reversed?
1/Keq (inverse)
What happens to the Keq when the reaction is multiplied by a coefficient?
The Keq is raised to that coefficient Keq^x
What happens to Keq when multiple steps of a reaction are added together?
Multiply the Keq values together
K1xK2xK3 = Keq overall
How do you calculate Keq?
- Look at the reaction (write it if it isn’t written out)
- Write the equilibrium expression
- Plug in the values at eq. (if not given, calculate)
What is the equation to convert between Kc and Kp?
Kp = Kc(RT)^change in n
What is the reaction quotient (Q)?
The same expression as Keq but at any point in time instead of just at equilibrium like Keq
What happens when Q is greater than the Keq?
The reaction will proceed to the left (reverse)
What happens when Q is less than Keq?
The reaction will proceed to the right (forward)
What happens when the Q and Keq are equal?
The reaction is at equilibrium
What is LeChatelier’s Principle?
- A reaction at equilibrium will stay at equilibrium unless exposed to a stress (concentration, pressure, temp.)
- If stressed, the reaction will shift in a direction that seeks to relieve that stress and reachieve equilibrium
How does the reaction shift if the concentration of one of the reactants is increased?
The reaction will shift to the right to use up the added reactant
How does the reaction shift if the concentration of one of the products is increased?
The reaction will shift to the left to use up the extra product
What happens if the concentration of a reactant is decreased?
The reaction will shift to the left to replace removed reactant
What happens if the concentration of a product is decreased?
The reaction will shift right to replace removed product
What happens to the reaction if the volume of the container is decreased?
The pressure of the inside of the container will increase, so the reaction will seek to decrease the pressure by shifting in the direction of the fewest moles of gas
What happens to a reaction if the volume of the container is increased?
The pressure of the inside of the container will decrease, so the reaction will seek to increase the pressure by shifting in the direction with the most moles of gas.
What happens if the amount of moles is the same on both sides of a reaction?
The reaction cannot shift to relieve stress
What will happen to a reaction if the overall pressure is increased by adding a nonreactive gas that is not part of the equilibrium reaction?
No shift or stress will occur because the partial pressures of the equilibrium components will remain the same
What happens to the reaction if heat is added during an endothermic reaction (heat is a part of the reactants)?
The reaction will shift to the right to use up the heat added
What happens to a reaction if heat is removed (cooling) during an endothermic reaction (heat is a part of the reactants)?
The reaction will shift to the left to make more heat.
What is the difference in the delta H value for an endothermic and exothermic reaction?
Endothermic - delta H is positive
Exothermic - delta H is negative
What happens to a reaction if heat is removed from an exothermic reaction (heat is a product)?
The reaction will shift to the right to make more heat.
What happens to a reaction if heat is added to an exothermic reaction (heat is a product)?
The reaction will shift to the left to compensate for the addition of heat?
What happens to the Keq during a temperature shift (heating or cooling)?
Endothermic:
Loss of heat - Keq gets smaller
Addition of heat - Keq gets bigger
Exothermic:
Loss of heat - Keq increases
Addition of heat - Keq decreases
What is an Arrhenius acid?
A compound that increases the amount of H+ ions in an aqueous solution
What is an Arrhenius base?
A compound that increases the amount of OH- ions in an aqueous solution
What is the Bronsted Lowry definition of an acid?
Acids are H+/proton donors and produce H+ ions in solution
What is a strong acid?
Dissociates completely in solution and produces maximum amounts of H+/H3O+ in solution (large Ka)
What are the 7 strong acids?
HCl, HBr, HI, HNO3, H2SO4, HClO4, HClO3
What is a weak acid?
Dissociates partially in solution and produces less H3O+/H+ (smaller Ka).
What is the definition of a Bronsted Lowry Base?
H+ acceptor, produces OH- in solution
What is a strong base?
Dissociates completely and produces maximum amounts of OH- (large Kb)
- Group 1 and 2 metal hydroxides are strong bases
What is a weak base?
Dissociates partially, produces less OH- in solution (small Kb). It goes to equilibrium instead of dissociating completely.
What pH intervals indicate a solution that is acidic, basic, or neutral
- pH less than 7 - Acidic
- pH of 7 or approximately 7 = Neutral
- pH greater than 7 - Basic
How do you calculate the pH or pOH of a strong species?
- Write the dissociation reaction
- Determine the relative concentrations of H+ and OH-
- Take the -log of either the H+ or OH- (H+ for acids, OH- for bases)
How do you determine the relative concentration of H+ or OH- if given pH?
[H+] - 10^-pH
[OH-] - 10^-pH
How do you calculate the pH of a weak species?
RICE table to get the [H+] at equilibrium. Then take the -log of the calculated [H+] to get the pH.
When can you ignore the -x when determining [H+]?
If the coefficient of the 10 in the Ka is -3 or less
What is a polyprotic acid?
- Acids with more than one ionizable (acidic) H+
- Acids ionize sequentially (one at a time)
What is different about the Ka in polyprotic acids?
- There are multiple Ka values for each step in the dissociation
- The Ka values progressively get smaller as H+ becomes harder to remove each time
- Most all of the H+ will come from the first dissociation (-log of first dissociation)
How do you calculate the pH of a weak base?
- Same way as with a weak acid
- Use a rice table to find [OH-] then take the -log of that concentration to determine pOH
- Subtract pOH from 14 to get pH
What kind of conjugate base does a strong acid have?
A super weak conjugate base (so weak it is considered negligible)
What kind of conjugate acid does a strong base have?
A super weak conjugate acid (so weak it is considered negligible)
What kind of conjugate base does a weak acid have?
A relatively strong weak conjugate base
What kind of conjugate acid does a weak base have?
A relatively strong weak conjugate acid
What is hydronium?
H3O+, created when a hydrogen ion combines with a water molecule
What is hydroxide?
OH-, results from a water molecule losing an H+
What does amphoteric mean?
Can react with both an acid or a base. Ex. Water (H2O)
What is salt hydrolysis?
- Some salts react with water to make the solution slightly acidic or basic
- Salts that do not react with water in this way are called neutral salts
How do you determine if a salt is acidic, basic, or neutral?
- Dissociate the salt into its respective ions
- Determine the parent acid (anion) or parent base (cation) of each ion
- Determine the strength of each parent species
- If parents are strong = super weak conjugates
If parents are weak = conjugates are relatively strong
What is a special quality of some metal cations?
Some metal cations can attract water molecules to become hydrated complex ions, then dissociate become H+ in solution
[Al(H2O)5]3+ —> Al(H2O)4 + H+
If both parent species are strong, what is the salt?
Neutral salt - the conjugates are non reactive
If the parent base is weak, what is the salt?
Acidic salt - stronger conjugate acid
If the parent acid is weak, what is the salt?
Basic salt - stronger conjugate base
If both parent species are weak, what is the salt?
Compare the Ka and Kb values
What is the common ion effect?
When any weak electrolyte (any species that produces ions in solution) is in solution in the presence of a common ion it will dissociate less than it would in pure water
What is a buffer?
Solutions that resist change in pH by being able to absorb/react with additions of acids or bases and maintain pH
(A weak acid or base and its conjugste partner)
What is buffer capacity?
The amount of acid or base a buffer solution can neutralize before its pH changes significantly
What are some examples of buffer systems?
Pools, fish tanks, your blood
What is a major component of a buffer system?
A buffer system contains roughly the same amount of a weak species and its conjugate
How do you calculate the pH of a buffer?
Write the dissociation reaction of the weak species, use a RICE table
(Place emphasis on the concentration of the common ion because it is a very important component of the buffer
How do you calculate the effects of adding acid/base stressors to buffers
- Identify the components of the buffer system
- Determine if stressor is H+ or OH-
- Determine which component of the buffer will react with (absorb) the stress
- Write the neutralization reaction between the buffer component and stressor
- BRA table to do the stoich to determine the new concentration of the species in the buffer
- RICE table with new values or HH equation to determine pH after occuring stress
What is a titration?
A technique used to determine the concentration of an unknown
What is a titrant?
A solution of known concentration used in titration
What is an analyte?
The substance being analyzed during a titration, the titrant is added into it
What is the equivalence point of a titration?
The point where exactly enough titrant is added to react exactly with the analyte, “neutralization”
What is the endpoint of a titration?
The point where the indicator changes color so you can tell the equivalence point has been reached
What is an indicator?
A substance put into a solution that changes color at a specific pH range to help identify the equivalence point
What is the half equivalence point?
The point where exactly half the analyte has been neutralized and the pH = pKa/pKb
