Chemical Equations

I. Writing Chemical Equations A.

Reactants Products

B. Balancing chemical equations

1) Numbers are written in front of each molecule so that there are the same number of each atom on both sides…these numbers are called coefficients

H2 + O2 H2O

H2 + O2 H2 O

2) It doesn’t matter which atom you decide to balance first

3) DO NOT change ANY subscripts

4) Subscript x coefficient = # of that atom

2 22 2

5) Recheck everything before you quit the problem

Try balancing these:

a) SO2 + O2 => SO322

b) Fe2O3 + H2 => Fe + H2O 323

c) C2H6 + O2 => CO2 + H2O 2 3

d) Aluminum carbonate + hydrochloric acid => aluminum chloride + carbonic acid

72

4 C2H6 + O2 => CO2 + H2O 672

d) Aluminum carbonate + hydrochloric acid => aluminum chloride + carbonic acid

II.Five basic Types of Chemical Reactions

1)Synthesis (composition)

2) Decomposition

3) Single Replacement

4) Double Replacement

5) Combustion

Before we begin …….

There are 7 elements that MUST be written with a subscript of 2 whenever they are by themselves in an equation:

I2

Br2

Cl2F2

O2

N2 H2

I

BringClayForOur

NewHouse

Br I N Cl H O F

1) Synthesis (composition)

* Template: A + X => AX

Clue 1: Only ONE product is formed

Clue 2 : Two elements as reactants

Clue 3 : metal oxide + water => metal hydroxide

Clue 4: non metal oxide + water => acid

Template: A + X => AX

Clue 1: Only ONE product is formed

Clue 2: Two elements as reactants

Examples:

2 Na + Cl2 => 2 NaCl

2 H2 + O2 => 2 H2O

1) Synthesis (composition)

Template: A + X => AX

Clue 3: metal oxide + water => metal hydroxide

Examples:

Na2O + H2O => 2 NaOH

calcium oxide + water => ???

CaO + H2O => Ca(OH)2

1) Synthesis (composition)

Template: A + X => AX

Clue 4: non metal oxide + water => acid

Examples:

CO2 + H2O => H2CO3

sulfur trioxide + water => ?????

SO3 + H2O => H2SO4

1) Synthesis (composition)

Practice:

a) K2O + H2O =>

b) N2O5 + H2O =>

c) Sodium is added to chlorine gas

d) Lithium oxide is added to water

1) Synthesis (composition)

* Template: AX => A + X Clue 1: metal chlorates => metal chloride + oxygen

Examples:

KClO3 => KCl + O2

barium chlorate => ??? + ???

Ba(ClO3)2 => BaCl2 + O2

(oxygen is proven by the glowing splint test)

2) Decomposition Reaction

2 2 3

3

Template: AX => A + X

Clue 2:

metal carbonates => metal oxide + carbon dioxide

CaCO3=> ??? + ???

CaCO3=> CaO+ CO2

(CO2 is proven by the flaming splint test)

2) Decomposition Reaction

Template: AX => A + X

Clue 3:

metal hydroxides=> metal oxide + water

Example:

Ca(OH)2 => CaO + H2O

2) Decomposition Reaction

Template: AX => A + X

Clue 4:

Two elements => separate elements

2 H2O => 2 H2 + O2

2 HgO => 2 Hg + O2

2) Decomposition Reaction

Template: A + BX => AX + B

AX + Y => AY + X

Clue 1: free metal replaces the “front”

element in a compound

Fe + CuSO4 => FeSO4 + Cu

Na + HOH => NaOH + H2

(metals replace the “front” element)

3) Single Replacement

2 2 2

2 Na + 2 HOH => 2NaOH + H2

(note how water is written)

NOT….

2 Na + H2O => Na2O + H2

ALERT!!!!!!

Template: A + BX => AX + B

AX + Y => AY + X

Clue 2: free non metal replaces the non

metal in a compound

Example:

Cl2 + NaBr => NaCl + Br2

3) Single Replacement

2 2

Template: AX + BY => AY + BX

Clue 1: two compounds are reacting

Examples:

AgNO3 + NaCl => AgCl + NaNO3

(switch the “front” elements)

lead (II) acetate is added to sodium iodide

Pb(C2H3O2)2 + 2NaI => PbI2 + 2NaC2H3O2

4) Double Replacement

Template: AX + BY => AY + BX

Clue 2: Double replacement reactions

always form one of these:

- a gas

- water

- a precipitate (something not soluble)

4) Double Replacement

Predicting what precipitate forms:

4) Double Replacement

COMPOUNDS SOLUBILITY

Alkali metals and ammonia Always soluble

Nitrates, chlorates, acetates Always soluble

Sulfates Soluble except with Ag+, Pb+2, Ba+2, Sr+2, Ca+2

Chlorides, Bromides, Iodides, Soluble except with Ag+, Pb+2, Hg+1

Carbonates, Phosphates, Hydroxides, Chromates, Sulfides

Never Soluble except with alkali metals and ammonia

Are these soluble?LiClyesCuOH noAgCl no

(NH4)2SO4yes

Na2CO3yes

Template: AX + O2 => AO + BO

Clue 1: Statement includes “burning”

which means to add oxygen gas

Example:

CH4 + 2 O2 => CO2 + 2 H2O

5) Combustion Reactions