We write reactions to represent what we think is happening at the microscopic level of atoms and molecules.

A + B + C ➝ Z

A + B ➝ X

X + C ➝ Z

Symbols

Stuff on top of arrows

Balancing

Rules

1. You can only put numbers out front.

   1. You can't add another copper to balance it unless you change the number out front

   2. CuCl2 can be turned into 2CuCl2 to get more coppers, but you can't do Cu2Cl2

2. Don't mess with the subscripts

   1. Change the numbers out front.

3. Treat "polyatomics" as one unit.

   1. PO4 is one unit. Don't break it down unless you need to.

4. Diatomic stuff can be broken down into half.

How to Balance

Total number of the product side has to equal the reaction side.

N2 + H2 ➝ NH3

N + H3 ➝ NH3

N2 + 3H2 ➝ 2NH3

KClO3 ➝ KCl + O2

2KClO3 ➝ 2KCl + 3O2

3Ca(NO3)2 + Al2(SO4)3 ➝ 3CaSO4 + 2Al(NO3)3

2C6H14 + 19O2 ➝ 12CO2 + 14H2O

C ➝ H ➝ O

Reaction Types

Combustion

In clean burning:

Fuel (solid, liquid, gas) + O2 (gas) ➝ CO2 (gas) + H2O (gas)

Combustion of propane:

C3H8 (propane) + 5O2 ➝ 3CO2 + 4H2O

Combination/Synthesis Reaction

Generally, smaller molecules that come together to form larger molecules

A + B ➝ C

Rusting of Iron:

Fe (solid) + O2 (gas) ➝ Fe2O3 (solid)

Haber process:

N2 + H2 ➝ NH3 (synthesis of ammonia)

Decomposition

(somewhat hard to tell what you'd get for products - how things fall apart is hard to get)

A ➝ B + C

Metal Carbonate

Typically, these happen with heating.

metal carbonate (heat) ➝ metal oxide + CO2

K2CO3 (solid) ➝ K2O (solid) + CO2 (gas)

Metal Chlorate

metal chlorate ➝ metal chloride + O2

KClO3 (solid) (heat) ➝ KCl (solid) + O2 (gas)

Metal Hydroxide

metal hydroxide ➝ metal oxide + H2O

Ca(OH)2 (heat) ➝ CaO (solid) + H2O (gas)

Metal Oxide

Metal oxide (heat) ➝ metal + O2

K2O ➝ K + O2

Single Replacement Reactions

A + XY ➝ AY + X

In order to determine how this reacts, you need to check solubility.

Fe (solid) + PbCl2 (aqueous) ➝ FeCl2 + Pb (solid)

Additionally, you need to make sure that the element that's on its own has higher activity than the one in the solution.

Ag (solid) + PbCl2 (aq) ➝ NO REACTION

Double Replacement

AB + XY ➝ AY + BX

AgNO3 (aq) + KI (aq) ➝ AgI (solid) + KNO3 (aq)

Irregularities

Diatomic Ions

• All halogens (Cl2, I2, Br2, F2)

• N2

• H2

• O2

• F2

• Cl2

• Br2

• I2

Formula List

Figure out how to get from words to... other stuff.

Elements are found on the periodic table.

Ionic compounds are found on the ion chart.

Acids (H2SO4) - figure out what the acid is

Hydrocarbons (organics - like propane)

Molecules - CO2, H2O, N2O

Net Reactions

Single Replacement Example

3Ca (s) + 2Al(NO3)3 (aq) ➝ 3Ca(NO3)2 (aq) + 2Al (s)

Break it down into separate ions.

3Ca (s) + 2Al (3+) (aq) + 6NO3 1- ➝ 3Ca (2+) + 6NO3 + 2Al

Cancel out spectator ions - atoms that exist

3Ca + 2Al (3+) ➝ 3Ca (2+).+ 2Al

Double Replacement Example

You can't split solid precipitates. Please don't try any of this at home

Ca(NO3)2 + Na2SO4 ➝ CaSO4 + 2NaNO3

Break it down into separate ions.

Ca (2+) + 2NO3 1- + 2Na 1+ + SO4 2- ➝ CaSO4 (s) + 2Na 1+.+ 2NO3 (1-)

Remove the redundancy.

Ca 2+ + SO4 2- ➝ CaSO4

Double Replacement Example 2 - Acid

NaOH (aq) + HCl (acid, aq) ➝ NaCl (aq) + H2O (l)

Na + OH + H + Cl ➝ Na + Cl + H + OH

OH- + H+ ➝ H2O

Double Replacement (why not) Example

CoCl2 + NaOH ➝ Co(OH)2 + NaCl

Co + OH ➝ Co(OH)2