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Equilibrium Flashcards

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1
Q

What is the imbalance that occurs between the forward and reverse reaction called?

A

Dynamic Equilibrium - Never fully becoming product, constantly moving back and forth

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2
Q

What is a Dynamic Equilibrium not mean?

A

The # of Reactant molecules = The # of Products Molecules

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3
Q

What is chemical equilibrium?

A

The conditions in which the concentration of all reactants and products eventually stop changing

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4
Q

For equilibrium to occur, what must happen?

A

Neither the reactants or products can leave the system so the direction of the chemical reaction is written is arbitrary

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5
Q

What are all the requirements of the system at equilibrium?

A
  1. System must be closed
  2. System must have constant temperature
  3. No change in macroscopic properties (no colour change, no emission of gas bubbles, no releasing of heat, etc.)
  4. Opposite reactions occur at the same time
  5. Equilibrium is attained by starting with either reactant or products
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6
Q

What are the three types of reactions?

A
  1. Reactants are favoured when % reactions is < 1%
  2. Products favoured when % of reaction is > 99% (the reaction appears to have gone to completion and is usually written as a one sided arrow)
  3. Reaction appears to be at equilibrium when the % of reactions is between 1%-99%
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7
Q

What is the equilibrium constant?

A

Used to relate the concentration of reactants and products in a mathematical and predictable way

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8
Q

What is the equilibrium constant expression?

A

K = Equilibrium constant
K = [Products]/[Reactants]

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9
Q

What is the generic reaction formula for the equilibrium constant?

A

aA+bB <- -> cC+dD
K = [C]^c [D]^d/[A]^a[B]^b

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10
Q

What are three things to remember when taking the generic reaction equilibrium constant?

A
  1. K depends on the way the equation is written
  2. Liquids and solids are not included into the equilibrium expression because their concentration is constant and has already been included to the equilibrium product constant
  3. K has a constant value at a given temperature, it does not depend on original concentration, volume of container or pressure
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11
Q

How does the Equilibrium constant expression relate to reaction rates?

A

k(f) = rate of the forward reaction
k(r) = rate of reverse reaction
At equilibrium k(f) = k(r)
Therefore, K = k(f)/k(r) and Keq (forward) = 1/Keq(reverse)

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12
Q

How does Temperature affect the Keq?

A

Changing the temperature favours either the forward or reverse reaction
This causes a shift in the Keq value, as well as a change in the [participants]
A new equilibrium will be reached with it’s own Keq value for the reaction at that temperature
At constant temperature, changing the equilibrium concentration does not affect Keq because the rate constants are not affected by the concentration changes
When the concentration of one of the participants is changed, the concentration of the others vary in such a way as to maintain a constant value for the Keq

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13
Q

What is the magnitude of Equilibrium Constants?

A

The magnitude of Keq is a measure of the extent to which a given reaction has or will take place
K»1: Equilibrium lies to the right; products are favoured
K«1: Equilibrium lies to left; reactants are favoured
K = 1: Half of the reactants have turned into products

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14
Q

How can you predict the direction of the reaction?

A

The reaction quotient, Q, is used to predict whether a system is at equilibrium
Reaction Quotient = Q = [PRODUCTS]/[REACTANTS]
Q = K → The system is at equilibrium
Q < K → in order to attain equilibrium, the reaction will move from left to right
Q > K → in order to attain equilibrium, the reaction will move from right to left

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15
Q

What is the hundred rule and why can we do it?

A

If you have a small K value the HUNDRED RULE can be used to approximate the concentration
Recall that as K«1, the reaction will hardly proceed in the direction of the products
That means that at this temperature, not too much reactant will be decomposed into the products.
We can assume that a the change in concentration is VERY SMALL (almost none) and insignificant

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16
Q

What is the Hundred rule and the 5% rule (Validations)?

A

Hundred rule: [Reactants]/K
If the resultant number is greater than 100, you can approximate the x value as zero
the assumption must be validated: Use 5% Rule
X/[Reactants]i
RULE: a difference of <5% justifies simplification

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17
Q

What is an Irreversible reaction?

A

This means the reactants turn into products, and the process cannot go backwards.

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18
Q

What is a reversible reaction?

A

Other chemical reactions are reversible.
This is where the products can turn back into the reactants under the right conditions.

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19
Q

What is Le Chatelier’s Principle?

A

Adding or removing a Reactant or Product
the addition of a reactant or product increases the concentration of said reactant/product
the equilibrium will shift in the direction that will consume the added component
Note: the addition of a pure solid or liquid does not cause a shift in equilibrium

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20
Q

How does a change in volume affect the reaction?

A

volume ↑ = pressure ↓
shift to the side with more moles of gas

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21
Q

How does adding gas affect the reaction?

A

adding an inert gas causes no shift in the equilibrium position as long as it doesn’t affect the concentration or partial pressure
Pressure depends on the number of gas molecules in the system.

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22
Q

How does temperature (in an exothermic reaction) affect the reaction?

A

Heat is like a product in an exothermic reaction because the reaction releases heat
If you add more heat, the system moves away from making even more heat
So the equilibrium shifts backwards towards the reactants
ΔH is (-)

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23
Q

How does the temperature (in an endothermic reaction) affect the reaction?

A

Heat is like a reactant in an endothermic reaction
This is because the reaction needs heat to make products
If you add morehear, it shifts the equilibrium to make more products
ΔH is (+)

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24
Q

How does a catalyst affect the reaction?

A

It helps the system reach equilibrium faster (since the reaction rates are increased) but does not change the equilibrium position
A catalyst speeds up both forward and reverse reactions equally. Why?
Because it lowers the activation energy by the same amount

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25
What is a catalyst?
Substance speeding up reactions without being used up.
26
What is a closed system?
System where no substances can enter or leave.
27
What is the definition of a dynamic equilibrium?
When forward and reverse reaction rates are equal.
28
What is the definition of Le Chatelier principle?
Rule predicting how a system adjusts to changes.
29
What is the solubility constant?
In a saturated solution, there is a dynamic equilibrium between the rate of dissolution and the rate of crystallization The solubility product constant (Ksp) is the equilibrium constant for the solubility equilibrium of a slightly soluble ionic compound
30
What are the conversions for the solubility constant?
Solubility of compound (g/L) ⇌ Molar Solubility of compound (mol/L) ⇌ Molar Concentrations of Ions ⇌ Ksp
31
What is the Common Ion Effect?
The Presence of a common ion will reduce the solubility of a substance A common ion occurs when two solutions containing the same ions are mixed together
32
What is Arrhenius' Theory of the acid and bases?
An acid is a substance that when dissolved in water increases the [H+(aq)] A base is a substance that when dissolved in water increases the [OH-(aq)]
33
What is the Bronsted-Lowry concept of acids and bases?
In a proton transfer reaction: An acid is a species donating a proton and a base accepts a proton Bronsted-Lowry acid must have a removable proton Bronsted-Lowry base have a pair of nonbonding electrons If it can donate or accept a proton, it is amphiprotic
34
What is the conjugate acid-base pair?
A conjugate acid-base pair consists of two species in an acid-base reaction, one acid and one base that differ by the loss or gain of a proton The more readily substance gives up a proton to the less readily conjugate base accepts
35
What is the Bronsted-Lowry theory on conjugate acid and bases?
A Bronsted-Lowry acid-base reaction can be thought of as a competition between the two bases in the system for protons The stronger base “wins” and forces the equilibrium in the direction of the weaker acid and base In any acid-base reaction, the equilibrium will favour the reaction that moves the proton to the stronger base The stronger acid, the weaker the conjugate base
36
What is ionization?
When acids are added to water they ionize into their ions Stronger acids, greater ionizations
37
What is dissociation?
Bases are added to water and they dissociate Stronger bases, greater dissociation
38
What is the acid ionization constant Ka?
HA(aq) + H2O(l) ⇌ H3O+ + A- The equilibrium constant expression for this is: Ka = [H3O+][A-]/[HA] The higher the value of Ka, the more acidic the solution The general expression can also be written in the following way HA(aq) ⇌ H+(aq) + A- Ka = [H+][A-]/[HA]
39
What are strong acids bases attributes?
These are strong electrolytes and exist as ions in aqueous solutions Their equilibrium lies far to the RIGHT They will yield very weak conjugates
40
What are monoprotic acids?
Have 1 proton to donate, example: HCl, HBr, HI, HNO3, HClO4
41
What are Diprotics?
Have 2 protons to donate, example: H2SO4
42
What are Triprotics?
Have 3 protons to donate, example: H3PO4
43
What are Oxyacids?
Acidic proton attached to oxygen
44
What are organic acids?
Have a carbon atom backbone (-COOH)
45
What are the attributes of weak acids/bases?
These only partially ionize in water They exist in solution as a mixture of molecules and component ions They are weak electrolytes Their equilibrium lies far to the left
46
What is the self ionization of water?
Self ionization (autoionization is a reaction in which two like molecules react to form ions In pure water, a few molecules act as bases and a few act as acids
47
What is the equilibrium constant of water, Kw, equal?
Kw = 1.0 x 10^-14
48
What is the standard Ka of water?
1.0 x 10^-7
49
What is the standard kb of water?
1.0 x 10^-7
50
What is the relations of Kw, Ka, and Kb?
Kw = (Ka)(Kb)
51
What is the pH scale?
pH = -log[H+] pH is used to describe the acidity of a solution pH = power or potency of hydrogen H+ = 10^-pH The pH scale is a numerical scale which, extends from 0 through to 14 It is based on the self-ionization of pure water Since the pH scale is a log scale with base 10, the pH changes by 1 for every power of 10 change in [H+]
52
What is the pOH scale?
pOH scale is used to measure [OH-] pOH = -log[OH-] OH- = 10^-pOH Relationship between pH and pOH pH + pOH = 14
53
How do we regularly measure pH? (less accurate)
For less accurate measurements litmus paper can be used “Red” paper turns blue above ~pH = 8 “Blue” paper turns red below ~pH = 5
54
How do we regularly measure pH? (More accurate)
For more accurate measurements, a pH meter is used which measures the voltage in the solution Electrolytes (dissociation of ions) will increase the voltage
55
What are Buffers?
Buffer/Buffer Solutions: An aqueous solution that resists changes in pH upon the addition of an acid or base. It contains either: A weak acid and its conjugate base A weak base and its conjugate acid It stays in an equilibrium mixture constantly because it is either a weak acid or base
56
What are Buffers actions?
The buffers purpose is to keep the pH range of a solution constant when small quantities of acid or base are added to the solution
57
What are the Characteristics of buffers?
Buffers always contain a mixture of a weak acid (or base) and its conjugate ion in solution Buffers maintain a neutral pH, other combinations of an acid (or base) and its conjugate maintain the pH at different pH values
58
What are Acidic Buffers?
Includes a weak acid and its conjugate base Acidic buffers (those based on a weak acid and a salt containing the conjugate base) generally have their buffering zone at pH below 7
59
What is the Buffer zone?
The “Buffer Zone” → An equivalent amount of unreacted reactants (weak acid/base) and its conjugated product (acid/base)
60
When or near the equivalence point, what happens to the pH?
When at or near the equivalence point, the pH changes drastically compared to halfway to the equivalence point
61
How do you prepare a buffer solution?
Buffer solutions are usually prepared by mixing a weak acid or base with a soluble salt containing the corresponding conjugate acid or base in approximately equal (molar) amounts By mixing the appropriate acid-salt or base-salt combinations, we can prepare buffer solutions with virtually any pH
62
What are buffers with higher pHs made from?
Buffers with higher pH can be made from a weak base and a salt containing its conjugate acid
63
How do Buffers work?
pH [H+(aq)] = Ka (Reactants/Remainder product) Concentrated buffer systems change very little in pH when H+(aq) or OH-(aq) is added Diluted Buffer systems change drastically in pH when H+(aq) or OH-(aq) is added
64
How do pH of Buffer solutions work?
Buffers are simply solutions of weak acids or bases and their respective soluble salts The pH calculations for buffers require exactly the same procedures used in studying acids, bases, and acid-base titrations
65
How does Bronsted Lowry's equations help us understand buffers?
Buffers contain relatively large concentrations of a weak acid and its conjugate base When an acid is added to a buffered solution (or either type), the hydrogen ions react essentially to completion with the weak base present When a base is added to a buffer, the hydroxide ions react essentially to completion with the weak acid present
66
What equations do we use to determine the pH of a buffer with a weak acid or base?
[base]/[conjugate acid] [acid]/[conjugate base] If the ratio remains virtually constant, the pH will remain virtually constant
67
How do you solve the addition of a strong acid/base buffer?
Deal first with the stoichiometry of the resulting reaction A strong acid will dissociate completely and react with the chemical entities present in solution After the stoichiometric calculations are completed, then consider the equilibrium calculations
68
What is the capacity of a buffer?
The buffering capacity of a buffer solution represent the amount of added hydrogen ions or hydroxide ions that the buffer can absorb without a significant change in pH A Buffer with a large capacity contains large concentrations of buffering components and so can absorb a relatively large amount of hydrogen ions or hydroxide ions and show little pH change
69
How can we determine the capacity of a buffer?
Determined by: [acid]/[conjugate base] The capacity of a buffered solutions is determined by the magnitudes of [acid] and [conjugate base]
70
How do calculate the buffer involving a weak acid?
HA(aq) →← H+(aq) +A-(aq) Ka = [H+][A-]/[HA The larger the value of Ka, the stronger the acid
71
What is the equation of the % ionization for solutions with weak acids?
Calculating the % Ionization for Solutions of Weak Acids p(percentage ionization) = [H+]/[HA]
72
How do you calculate the pH for polyprotic acids?
Polyprotic Acids ionize one proton at a time Ka for each equilibrium
73
What are the Acid Base Properties of a Salt Solution?
Salt solutions can be acidic, basic, or neutral It depends on the ions that are produced in hydrolysis
74
What are the general rules about salt solutions?
Strong acids and strong bases have weak conjugates Salts that consist of cations of strong bases and the anions of strong acids have no effect of the pH Group 1 and Group 2 metals ions exhibit NO acid base properties Water will have relatively little acid-base effect Anions act as bases Cations act as acids When a solution contains both the conjugate base of a weak acid and the conjugate acid of a weak base, the effect on pH depends on the value of Ka and Kb If Ka > Kb solution will be acidic If Kb > Ka solution will be basic If Ka = Kb solution will be neutral
75
When is a salt going to produce a neutral solution?
When both the conjugate acid makes a strong base and the conjugate base makes a strong acid when the salt is mixed with water
76
What is a titrant?
The solution in the burette (known)
77
What is a sample?
The solution being analysed in titration (unknown)
78
What is the Equivalence point?
When moles of H+ = Moles of OH-
79
What is the endpoint?
The point in a titration when the colour change takes place
80
What is the primary standard?
A very pure and accurate concentration of a chemical. It is used to standardize the titrant. Standardize means to determine its exact concentration.
81
What are the 3 types of titrations
1) Strong Acid/Strong Base 2) Weak Acid/Strong Base 3) Strong Acid/Weak Base
82
What are titration curves?
Graphical representation of a titration It plots the pH of solution vs the concentration of the titrant It tells us the pH at the equivalence point
83
How do you solve Strong base and Strong acid titrations?
The pH of the solution will be 7 because at neutralization, the pH is determined by the auto-ionization of water (the conjugates of the strong acid and base cannot hydrolyze)
84
How can you solve weak acid/base titrations?
In Weak acid strong base problems, there are two separate problems to solve A stoichiometry problem (determining the limiting reagent) An equilibrium problem (examine major components after the reaction takes place to determine a dominant equilibrium)
85

Chemistry 12 (1 decks)

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