The process in which the physical and

chemical properties of the original

substances change to new substances

with different properties atoms are rearranging in new ways

Chemical Reaction

Characteristics of chemical reactions

• Reactant= a substance that enters into a chemi-

cal reaction• Product= a substance that is produced by a chemi-

cal reaction

Types of reactions• Synthesis(combination) 2 or more reactants

combine to produce a new substance

• Decomposition 1 reactant breaks down into 2 or more new substances

• Single-replacement an element replacing a similar element in the other reactant

• Double-replacement cations and anions of two different compounds change places

• Combustion- A hydrocarbon is combined with oxygen gas to make Carbon dioxide and water

Examples

Synthesis: A + B AB

• Write the Reaction that is Occuring

Decomposition: the opposite of a synthesis reaction - a complex molecule breaks down to make simpler ones. These reactions come in the general form:

• AB A + B

• Write the Reaction that is occuring

Single replacement: These reactions come in the general form of:

• A + BC ---> AC + B

• Write the Reaction that is Occuring

• Note:

– In single replacement reactions, “Like replaces like!”

– What this means, is that metals replace metals or cations, nonmetals replace nonmetals, or anions!!

It’s a bit like cutting in at a dance!!

Double replacement: These reactions are in the general form:

• AB + CD AD + CB

• Write the reaction that is occuring

It’s a bit like changing your partners in square dancing!!

One more type

• Combustion-a hydrocarbon combines with oxygen gas to produce carbon dioxide and water. CxHy + O2 CO2 + H2O

• It is also called “burning.”

Lets see if you can apply these 5 types of reactions to the equations listed below:

• 1)  2NaOH + Cu(NO3)2 --> 2NaNO3 + Cu(OH)2

• 2)  CH4 + 2O2 --> CO2 + 2H2O

• 3)  Fe + 3NaBr --> FeBr3 + 3Na

• 4)  MgSO4 + BaCl2 --> MgCl2 + BaSO4

• 5)  2Pb + O2 --> 2PbO

• 6)  Na2CO3 --> Na2O + CO2

Let’s look more closely at reactions where a precipitate is formed.

• when an Ionic Compound is dissolved in water the ions are separated and are surrounded by water molecules (aqueous).

• When two Ionic Compounds are combined and a precipitate forms, one of the two new combinations of ions has formed a compound that water is not able to break apart It is insoluble. You must label that it has become a solid.

when solutions of sodium iodide and mercury(II) chloride

Example

What type of reaction is this? What will the products be?

NaI(aq) + HgCl2(aq)

NaCl( ) + HgI2( ) If you see that a precipitate forms then one of the products must be written as a solid.

If I tell you that NaCl is in solution, The solid must be HgI2

Dissociation

• Shows what happens when an ionic salt dissolves in water.

Ex. NaI(s) ----> Na+(aq) + I-(aq) HgCl2(s) ----> Hg2+(aq) + 2Cl-(aq)

*Notice ions are free floating and do not form diatomic molecules

“Net ionic equation”

• Sometimes you may want to show just the product that is actually forming a solid

• Hg2+(aq) + 2I-(aq) HgI2(s)

• This is called the “net ionic equation”

3 Ways to Show the Reaction

1. Chemical equation

NaI(aq) + HgCl2(aq) NaCl(aq) +HgI2(s)

2. Complete ionic equationNa+(aq) + 2I-(aq) + Hg2+(aq) + 2Cl-(aq)

Na+(aq) + Cl-(aq) + HgI2(s)

3. Net ionic equation (eliminate “spectator” ions)

Hg2+(aq) + 2I-(aq) HgI2(s)

Since the “spectator” ions don’t change during the reaction, the net ionic equation is an accurate representation of the chemical change that is occurring.

How can you predict which substance will form a precipitate?

• Purpose: To determine rules for when Precipitates are formed

• Procedure: Add a drop of each compound into the transparency. Record which form Precipitates. Come up with patterns about what it takes for something to be a “precipitate”

Write the Dissociation reaction when Sodium Clhoride Dissolves in Water

Write The Net Ionic Equation of the formation of Lead(II) Chloride.

• What patterns did you come up with?

• Thus you would write the formula like this

• NaI(aq) + HgCl2(aq) NaCl( aq ) + HgI2(s )

Silver nitrate solution combined with sodium hydroxide solution produces a precipitate.

Example

AgNO3(aq) + NaOH(aq)

AgOH( ) + NaNO3( )

AgOH is not soluble

ThusAgNO3(aq) + NaOH(aq)

AgOH(s) + NaNO3(aq )

Your Job…

• Using the “Solubitilty Rules” Write the Net ionic and Molecular Equation for Each of the Reactions!

For the Following: Write the Molecular Formula, Determine if

a reaction will occur and if so write the Net- Ionic Equation

• Ni (NO3)2 (aq) + BaCO3 (aq)

• Fe2O3 (aq) + ZnCO3(aq)

• H2S (aq) + KOH (aq)

. Na3PO4 (aq) + ZnSO4 (aq)

Now you are ready to describe how copper metal can change form!

Could you change copper wire into Copper Sulfate? Could you Change it back into copper wire?