Chemical

Reactions.

Equilibrium.

Acids &Bases

Oxidation Number

Charge of an atom or a group of atoms

Also known as Valence

Ex: NaCl, Na+ and Cl-

H2SO4, H+, S+6 and O-2

Writing formulas When the oxidation numbers of the atoms in a

compound are known, we can write the chemical formula of that compound. Ex: H+ and O 2- form H2O (sum of oxidation

numbers in a neutral compound should be 0)

When knowing the formula of a chemical compound, we can find the oxidation numbers of the atoms in that compound. Ex: H2SO4 H always +1, O always +2, so

2x (+1) + 4x (-2) = -6. Since H2SO4 is neutral, S has to be +6.

Chemical Reactions

5 types:

1. Combination Reactions

2. Combustion Reactions

3. Decomposition Reactions

4. Single-replacement Reactions

(Displacement)

5. Double-replacement Reactions

(Metathesis)

Combination Reactions

formation of a compound from two or

more substances

Ex:

2Na (s) + Cl2 (g) 2NaCl (s)

CO2 (g) + H2O (l) H2CO3 (l)

Combustion Reactions

reaction of substances with O2 usually accompanied by the release of

large amounts of heat (Q)

Decomposition Reactions

one compound decomposes or splits to

form two or more simpler compounds

and/or elements.

Ex:

CaCO3 (s) CaO (s) + CO2 (g)

H2CO3 (l) H2O (l) + CO2 (g)

Single-replacement Reactions

An element reacts with a compound, and

results in the displacement of an element

or group from the compound.

Ex:

Na(s) + HOH (l) NaOH (aq) + H2 (g)

Na (s) + HCl (g) NaCl (s) + H2 (g)

Double-replacement

Reactions

exchange of two groups or two ions

among the reactants

Ex:

NaOH (aq) + HCl (aq) NaCl (aq) + HOH(l)

Balancing Simple Equations Ex: 4Al+ 3 O2 2 Al2O3

Al=1 x4= 4 Al=2 x2= 4

O=2 x 3= 6 O=3x2 = 6

2Na + H2SO4 Na2SO4 + H2

Na=1x2=2 Na=2

H=2 H=2

S=1 S=1

O=4 O=4

Oxidation-Reduction

Reactions

Oxidation-reduction (redox) reactions

involve the transfer of electrons from one

compound or species to another.

Oxidation is the process by which an

atom or species loses its electrons.

Reduction is the process by which an

atom or species gains electrons.

Oxidation-Reduction

Reactions

Ex:

2Fe + 3Cl2 2 FeCl3

Fe0 Fe3+ + 3e- oxidizing 3 2

6

2Cl0 + 2x 1 e-2 Cl- reducing 2 3

Oxidation-Reduction

Reactions

Ex:

3Cu0 + 8H+N+5O3-2 3Cu+2(N+5O3

-2)2-1 + 2N+2O-2 +

4H+2O-2

Cu0 Cu+2 + 2 e- 2 3

6

N+5 + 3 e- N+2 3 2

Solutions Solution = one solvent with one or more

solutes.

Mixing states or same state

Water-based solutions: the solvent is water.

Solubility=the amount of the substance that will dissolve in a particular solvent.

"like dissolves like : water is polar, will dissolve polar or ionic

substances

Non-polar substances will be soluble in non-polar solvents (ex CCl4)

Solutions

Concentration:

c%=

x 100 (%)

md= mass of dissolved substance (g),

ms=mass of solution (g)

Molarity

C=

(moles/l, M) ,

=nr. of moles,

V=volume of the solution (l)

Solutions

Molality

C=

(moles/kg)

=nr. of moles,

ms=mass of the solvent (kg)

Normality

CN =

(Eg/l) CN=nxCM

Eg= gram equivalents n is nr. of H+, OH-, e-

V=volume of solution

Equilibrium

Reversible reactions are reactions in

which there are both forward and

backward reactions.

Ex:

CH3OH+ CH3COOH CH3COOCH3 + H2O

back-and-forth directional changes take

place until the reaction mixture reaches

the equilibrium!

Equilibrium

equilibrium constant (Kech) of a reversible

reaction is equal to the ratio of the

product of the concentrations of the

products raised to their corresponding

coefficients, to the product of the

concentrations of the reactants raised to

their corresponding coefficients.

Ex:

a A+ b B c C + d D

Kech=

Le Chateliers Principles lf we change the conditions factors

(concentration, pressure, temperature) of a reaction system in equilibrium, the system will shift in such a way as to reduce the imbalance caused by the stress.

Ex: N2 (g) + 3H2(g) 2 NH3 (g) + Q A raise in concentration of N2 will shift the

system to the right

A raise in pressure will shift the system to the right

A raise in temperature will shift the system to the left

Acid-Base Equilibrium 3 theories:

Arrhenius Definition:

Acid increases H+ ions in an aqueous solution

Base increases OH- ions in an aqueous solution

The Bronsted-Lowry Definition

acid proton donor,

base proton acceptor.

The Lewis theory

Lewis acid accepts a pair of electrons

Lewis base donates a pair of electrons

Ex:

Hl + H20 H3O+ + l- (gives protons)

Acid Conjugated

Base

NH3+H2O 4++ HO- (accepts protons)

Base Conjugated

Acid

Concept of pH

pH shows the acidity of a solution and is

defined as log [H3O+]

pOH is complementary, and shows the

basicity of a solution and is defined as

log[HO-]

Ionization of water

H2O + H2O H3O+ + HO-

Kech = 3

+[

]

22 , but since H2O is

considered constant, Kechx[H2O]

2=Kw=[H3O+][HO-], Kw is defined

as the ion-constant product of water, and

has the value of 10-14 (mol/l)2

When we apply a logarithm to the

expression we get:

log Kw = log [H3O+]+ log [HO-].

If we multiply by (-1), we get:

-log Kw = - log [H3O+]+ (- log [HO-]),

So 14= pH + pOH.

Strong Acids. Strong Bases Strong acid= one way reaction (not

equilibrium)

HA+H2O H3O+ + A-

pH= - log [H3O+] = -log CHA

Strong base= one way reaction (not equilibrium)

B+H2O OH-+ BH+

pOH= - log [HO-] = -log CB Ex: strong acids: HCl, H2SO4 strong bases: NaOH, KOH

Weak Acids

Weak acid= equilibrium reaction

HA+H2O H3O+ + A-

Kech= 3

+[]

2 [] , since we can consider [H2O]

constant,

Kechx[H2O]=Ka= 3

+[]

[], where Ka is the acidity

constant.

Ex: citric acid (lemon), acetic acid (vinegar)

Weak Acids pH = - log [H3O

+]

[H3O+]=

[]

[]

, but [H3O+]= [A-],

So [H3O+]2=Kax[HA]

[H3O+]=

pH= -log

pH=-1

2logKaxCHA

pH= -1

2 log Ka -

1

2 log CHA

-log Ka= pKa,

So pH=

pKa -

log CHA

Weak bases

Weak base= equilibrium reaction

B+H2O BH+ + OH-

Kech=

+[

]

2 [] , since we can consider

[H2O] constant,

Kechx[H2O]=Kb=

+[

]

[], where Kb is the

basicity constant.

Ex: ammonia, NH4OH.

Weak Bases pOH = - log [HO-]

[HO-]= []

[+], but [HO-]= [BH+],

So [HO-]2=Kbx[B]

[HO-]=

pOH= -log

pOH=-1

2logKbxCB

pOH= -1

2 log Kb -

1

2 log CB

-log Kb= pKb,

So pOH=

pKb -

log CB

pH+pOH=14,

So pH= 14- (

pKb -

log CB )

Buffer Solutions

solutions which resist changes in pH when small amounts of acid or base are added

usually a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.

Ex: plasma is a buffer solution (complex system with more than one acid/base, the most important one being the H2CO3/HCO3

- couple)

For a weak acid-conjugated base:

pH=pKa+log[ ]

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For a weak base-conjugated acid:

pOH=pKb+log[ ]

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