Chemistry Unit 2 (Chapters 13 & 14)

Chapter 13- Fundamental Equilibrium Concepts, Chapter 14- Acid Base Equilibria

Equilibrium

the concentrations of reactants and products remains constant and the rates of the forward and revers reactions are equal

Reversible reaction

double arrow means that reactants can convert to products, and products can convert to reactants

Reversible reactions subtend toward ______

equilibrium, will keep going until equilibrium

Reaction Quotient (Q)

helps you determine the status of a reaction using pressure (Qp) or concentration (Qc), tells you the relative ratio of product to reactant

A larger Q means

more products

A smaller Q means

more reactants

Qc expression general format

Q = [C]^y [D]^y / [A]^m [B]^n

Qp expression general format

Pc ^x Pd ^y / Pa ^m Pb ^n

The constant Q exhibited by a system at equilibrium is

the equilibrium constant (K)

K values > 1 indicate

favoring products

K values < 1 indicate

favoring reactants

If K = 1, then

the ratio of products/reactants is equal!

What is omitted from the Qc expressions?

solids and liquids

Does equilibrium imply that you have the SAME concentrations of products and reactants?

No, equilibrium only implies same RATE of rxn in both forward & reverse rxns, unless k =1

If Q > K

the reaction is currently favoring products, must push to left/REVERSE direction, toward reactants

If Q < K

the reaction is currently favoring reactants, must push to right/FORWARD direction, toward products

If Q = K

reaction is at equlibrium

Le Chatlier’s Principle

if an equilibrium is stressed or altered, the system will experience a shift in response to the change that re-establishes equilibrium, basically equilibrium wants to be retained

How can equilibrium be reestablished?

-Increase/Decrease in products or reactants

-Pressure

-Temperature

How do you convert from a Kp to Kc expression?

Kp = Kc (RT)^delta n

R = gas constant (0.08206 l*atm/mol*k)

T = temperature (K)

delta n = change in moles of gases (n product - n reactant)

What determines what happens to K?

depends on if reaction is endothermic or exothermic!!!

What are ICE tables used for?

allows you to determine what the concentrations are at equilibrium for a reversible reaction, given initial values

ICE

Initial, Change, Equilibrium

When can you assume X is small?

if K is less than or equal to 10^-5 and the reaction is headed to RIGHT (making product)

if K is more than or equal to 10^-5 and the reaction is headed to the LEFT (making reactant)

What is the Bronsted-lowry definition of acids and bases?

Acids: Donate a proton (H+)

Bases: Receive a proton (H+)

What are conjugates?

-Conjugates are always on the product side!

-Acid always becomes conjugate base (species that remains when acid donates H+)

-Base always becomes conjugate acid (species that remains when base receives H+)

Will a bronsted lowry acid always be a lewis acid?

A bronsted lowry acid/base will always be a lewis acid/base, but not all lewis acid/bases are bronsted lowry

Lewis (think LONE) Acids & Bases

Acid: ACCEPTS a lone pair

Base: DONATES a lone pair

Amphoterism

when something is capable of donating or accepting H+/ donating or accepting lone pair (Can act as both an acid or a base)

Autoionization

can ionize by itself

Equilibrium Constant (Kw) for auto ionization of H2O at RT

Kw = 1.0 ×10^-14

since K < 1, rxn favors reactants

Neutral pH

when you have an equal amount of OH- and H3O+

Acidic pH

abundance of H3O+, low pH

Basic pH

abundance of OH-, high pH

pH

used to measure acidity & basisity

For the rxn to be at equilibrium, Kw must be at

1.0×10^-14 at 25 C

What is the impact of temperature on Kw?

As temperature increases, Kw increases

How do you find the pKw?

pKw = -log (Kw)

What are the 6 strong acids?

1. HCl

2. HBr

3. H2SO4

4. HI

5. HClO4

6. HNO3

What are the 6 strong bases?

1. NaOH

2. LiOH

3. KOH

4. Ca(OH)2

5. Sr(OH)2

6. Ba(OH)2

Acid Ionization Constant (Ka)

equilibrium constant that tells you the strength of an acid

Base Ionization Constant (Kb)

equilibrium constant that tells you the strength of a base

Template acid Ka reaction

HA (aq) + H2O (l) ⇌ H3O+ (aq) + A- (aq)

Ka equation for an acid

Ka = [H3O+][A-] / [HA]

Template base Kb reaction

B + H2O ⇌ HB+ + OH-

Kb equation for a base

Kb = [BH+][OH-] / [B]

[BH+] = conjugate acid of the original base

[OH-] = conjugate base of H2O

[B] = original concentration

Strong acids vs weak acids

Weak acids: partially ionize/dissociate, reversible

Strong acids: fully ionize/dissociate, NOT reversible

Percent Ionization

a quantitive measure of how much ionization occurs, the larger the % ionization is, the stronger the acid

Percent Ionization of an acid

% ionization = [H3O] eq/ [HA]0 × 100

Percent Ionization of a base

% ionization = [OH-] eq/ [B] 0 × 100

The stronger the acid, the ____ the conjugate base.

weaker

At room temperature, an conjugate acid-base pair must always

have their Ka Kb equal to Kw, Kw = Ka * Kb

Acid strength trends

• Acid strength increases down a group on Ptable, and left to right

• Acid strength increases with oxidation state (think oxyacids)

Oxyacids

an acid that contains an oxygen atom bonded to a hydrogen atom and at least one other element

Acidic salt

salt that generates acidic ions

Basic salt

salt generates hydroxide ions

Buffers

weak acid and its conjugate base, solutions containing an appreciable amount of weak conjugate acid base pair

Buffer capacity

the amount of acid or base that can be added to a buffer before pH changes significantly

Common Ion effect

If introducing the same ion as the one present, the concentration decreases for the compound with the common ion

Henderson - Hasselbach Equation

pH = pKa + log ([A-]/[HA]

pH = pH of a buffer mixture

pKa= acid of the conj. acid-base pair

[A-] = conjugate base

[HA] = conjugate acid