When a chemical reactionoccurs, there is ALWAYSa change in propertiesAND energy

• Color change• Heat change• Gas produced• Precipitate formed

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Chemical Reactions - 3 min

There are 5 basictypes of chemicalreactions:

Two simple substances combine to form a more complex one.

element + element compound

Examples:

2H2 + O2 2H2O

6CO2 + 6H2O C6H12O6 + 6O2

A complex substance breaksinto simple substances.

compound element + element

Examples:

2H2O 2H2 + O2

2KClO3 2KCl + 3O2

A single element replacesan element in a compound.

element + compound element + compound

Example:

Zn + 2HCl H2 + ZnCl2

Two different elements in twodifferent compounds switch places.

compound + compound compound + compound

Example:

H2SO4 + 2NaOH Na2SO4 + 2HOH

A hydrocarbon reacts with oxygento form carbon dioxide and water.

Example:

CH4 + O2 CO2 + H2O

An acid and base react to form a salt and water

acid + base salt + water

Example:

2HCl + Mg(OH)2 MgCl2 + 2H2O

Any reaction in which elements change oxidation number.

Example:

S + O2 SO2 0 0 -2

Example:

S + O2 SO2 0 0 -2+4

Aqueous reactions that involve the formation of a precipitate,an insoluble substance.

Example:

2KI(aq) + Pb(NO3)2(aq) 2KNO3(aq) + PbI2(s)

Physical State Symbols: (aq) = aqueous (g) = gas (s) = solid (cr) = crystal (l) = liquid

Predicting Reaction Products

Predicting Reaction Products

Atoms can be neithercreated nor destroyedin ordinary chemicalreactions...

so there must be thesame number of atomson both sides ofthe equation.

Subscripts represent thenumber of atoms ineach molecule.

2H2O 2H2 + O2

Coefficients represent thenumber of molecules.

2H2O 2H2 + O2

To determine the totalnumber of atoms,multiply the coefficientby the subscript.

2H2O 2H2 + O2

H2SO4

There are ___atoms of hydrogen.

H2SO4

There are ___atoms of hydrogen.

2

H2SO4

There are ___atoms of oxygen.

H2SO4

There are ___atoms of oxygen.

4

Al2(SO4)3

There are ___atoms of oxygen.

There are ___atoms of oxygen.

12

Al2(SO4)3

2 Na2O2

There are ___atoms of sodium.

There are ___atoms of sodium.

4

2 Na2O2

2 Ca3(PO4)2

There are ___atoms of phosphorus.

4

2 Ca3(PO4)2

There are ___atoms of phosphorus.

2 Ca3(PO4)2

There are ___atoms of oxygen.

16

2 Ca3(PO4)2

There are ___atoms of oxygen.

6 CaSiO3

There are ___atoms of calcium.

6There are ___atoms of calcium.

6 CaSiO3

Balancing equationsby inspection

The order in whichthese seven steps are performed is important.

While there AREshortcuts, and you willlearn about one, ...

following these steps inorder is the best way tobe sure you are correct.

Check for diatomic molecules.

H2 - N2 - O2 - F2 -Cl2 - Br2 - I2

Balance the Metals

DO NOTinclude H

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Balance the Nonmetals

DO NOTinclude O

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Balance Oxygen

Balance Hydrogen

Balance Hydrogen

Recount All Atoms

This is done to find any counting mistakes!

Recount All Atoms

If the atoms are NOT balanced, there is aproblem somewhere. Work your way back up the steps, from bottom to top,

until you find the problem and fix it.

If every coefficient in theequation will reduce,rewrite the equation withreduced coefficients.

If there is a coefficientof 1 - the equationcannot be reduced.

Balancing Equations