Equilibrium Constants

K_eq= [Products]/[Reactants]
For example, the formula of:

Fe³⁺_(aq) + SCN^-⇋ FeSCN²⁺_(aq)

K_eq=[FeSCN²⁺]/[Fe³⁺][SCN^-]

N₂O_4(g)—> 2NO_2(g)

forward rate=K_t[N₂O₄]

2NO_2(s)—>N₂O_4(g)

reverse rate=K_r[NO₂]²

N₂O_4(g)⇋ 2NO_2(g)

rate forward=rate reverse
K_f[N₂O₄]=K_r[NO₂]²

K_f/K_r=[NO₂]²/[N₂O₄] Law of mass action equation

Q=[NO₂]²/[N₂O₄]
Q is reaction quotient

At equilibrium “eq”
Q=K_f/K_r=[NO₂]²_eq/[N₂O₄]_eq=K_eq
K_eq =equilibrium constant

aA+bB⇋ cC+dD

Q=[C]^c[D]^D/[A]^a[B]^b Law of mass action

Equilibrium occurs when the forward rate is equal to the reverse rate

Equilibrium is dynamic - there is still reaction happening. It’s just balanced

O₃⇋ O+O₂
H₂O⇋ H⁺ OH^-
Fe + O₂ —> Fe₂⁺³ O₂

Magnitude of K_eq

CO(aq)+CI₂ (g) = COCI₂(g)

K_eq=[COCI₂]/[CO][CI₂]=4.56×10^9

K>1 greater products than reactants

K<1 greater reactants than products.

COCI₂(g)=CO(aq)+CI₂ (g)

K_eq=[CO][CI₂]/[COCI₂]=2.142×10^-10=1/K_eq=1/4.56×10^9

If you reverse the direction the K_eq is inverse

N2O4(g)=2NO2(g)
Keq1=[NO2]²/[N2O4]
2N₂O=4NO₂(g)

K_eq2=[NO₂]⁴/[N₂O₄]²

K_eq2=K_eq1²

If a reaction is multiplied by a constant then the K_eq is raised to that power.

2NOBR(g)=2NO(g)+Br₂(g) Keq₁

Br₂(g)+CI₂(g)=2BrCl(g) Keq₂

2NOBr(g)+Cl₂(g)=2NO(g)+2BrCl Keq₃

K_eq3=K_eq2=K_eq1

If you add reactions together K_eq is equal to individual K_eq multiplied

K_a

The acid-dissociation constant. The equlibrium constant related to weak acids.

K_b

Base dissociation constant. The equlibrium constant related to weak bases.

General Form

HA ⇋ H⁺ + A^-
For ex:) HCI → H⁺ + Cl^-

Table of Acid with Ka and pKa Values (7 you need to know)

Acid HA A^-

Hydroiodic HI I^-

Hydrobromic HBr Br^-

Perchloric HCIO₄ CIO₄^-

Hydrochloric HCI Cl^-

Chloric HCIO₃ CIO₃^-

Sulfuric(1) H₂SO₄ HSO₄^-

Nitric HNO₃ NO₃^-

pH=-log[H^-]

The pH is a method of reporting hydrogen ion concentration.
pH is 7
Acidic pH is below 7
Basic pH is above 7
Only the digits after the decimal point are sig figs in logarithms