Equilibrium

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Chemical Equilibrium

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Definitions

Bronsted-Lowry base: must recieve an H+

Arrhenius base: gives up an OH-

pKb= -log(kb)

Equilibrium

Acids

Acid base titrations (Weak acid in this example)

Buffer system

Acid added neutralizes the conjugate pair base Base added neutralized the conjugate pair acid

pH = pKa of weak acid

Must require an acid base conjugate pair

Used to stabilize the pH of a solution

n acid=n base

Solution is neutral when this has been achieved

CaVa=CbVb

Used to find amounts of acid in a solution through neutralization

ph indicators

If done correctly, the ph indicator will change colour at the equivalence point. If not, it may change too soon, leaving the equivalence point unsolved for.

After equivalence point

Intial [OH-] from excess base

at equivalence point

Weak acid is neutralized, turns into a conjugate base

Before equivalence point

Excess weak acid

Before base is added

Disassociation of weak acid in H2O

Written as HA

Becomes A- when it loses it's hydrogen

Ha+H2O→H3O+ + A-

polyprotic acids

First disassociation has largest Ka

Next disassociation progressively has smaller Ka

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

Ka= acid disassociation constant

pH <7

pH= -log(H3O) (H3O)=10^-pH

pH+pOH= 14

Types

Weak acids

Can calculate %disassociation... often 1%

Strong acids

100% disassociation Ex: HCl, HBr, HI

pKa= -log(Ka)

Alkaline (Base)

Keq=Kb=[BH+][OH-]/[BOH]

Keq

Ksp

Hard vs soft water Kidney stones

Crystallization of cations and anions.

sped up by larger surface area= faster to eq

Dissolution of salt crystals

At Eq, solids stop dissolving

common ion effect

Higher ksp= more soluble Used on highly insoluble salts

Due to large amounts of H2O already present, we ignore H2O in Keq expressions, as it will not greatly impact the outcome of concentration.

When [P] and [R] stabilize, equilibrium is reached

Le chatelier's principle

When conditions change, eq is changed

Ex: changed in pressure, temperature are counteracted

Ex: gas exchange in the lungs

Pressure lowers, concentration lowers

Temperature speeds up forward and reverse reactions

Dynamic equilibrium

Forward and reverse actions are constant Reactions re reversible

Easier in a closed system

phase equilibrium

Ice tables(concentrations at EQ)

Used to solve for x, using stoichiometry.

[C]^c[D]^d/[A]^a[B]^b

When Keq>1, the forward reaction is favored When Keq<1, the reverse reaction is favored

Kf/Kr

Affected by delta H and temperature

Kb = base disassociation constant

pH >7

Conjugate pairs

Stronger acid = weaker conjugate base Stronger conjugate base = weaker conjugate acid

pKa+pKb at 25 degrees = 14

Ka*Kb=Kw=10^-14

Connects acids and bases through the gain and loss of a proton

Ex: H2CO3 → HCO3

[OH-]= 10^-pOH pOH= -log[Oh-]

Strong bases

Alkali metal hydroxides (Group two) Though they have low Ksp

Lower pH and smaller Ksp

Alkali metal hydroxides (Group one)

Highly soluble in water and high pH