Chapter 8 Notes, Part IChapter 8 Notes, Part I

Parts of an equationParts of an equation

Types of reactionsTypes of reactions

What is a chemical reaction?What is a chemical reaction?

• A chemical reaction is the act of A chemical reaction is the act of changing substances into new changing substances into new substances with new and substances with new and different chemical and physical different chemical and physical properties.properties.

A Chemical EquationA Chemical Equation• A chemical equation shows what A chemical equation shows what

is going on in a chemical is going on in a chemical reaction.reaction.

• Instead of writing down the Instead of writing down the entire sentence “hydrogen entire sentence “hydrogen reacts with oxygen to form reacts with oxygen to form dihydrogen monoxide (water)”, dihydrogen monoxide (water)”, you could write…you could write…

2H2 + O22H2O

reactantsreactants

productsproducts

The substances you have before a chemical The substances you have before a chemical reaction occursreaction occurs

The substances you have after a chemical The substances you have after a chemical reaction occursreaction occurs

(found on the left side of the equation)(found on the left side of the equation)

(found on the right side of the equation)(found on the right side of the equation)

2H2 + O22H2O

subscriptssubscripts

coefficientscoefficients

How many elements are in a compoundHow many elements are in a compound

How many substances are in the How many substances are in the reactionreaction

2H2 + O22H2O

The arrow reads as “produces”, “yields” or “reacts to form”The arrow reads as “produces”, “yields” or “reacts to form”

4Fe + 3O22Fe2O3

Iron reacts with oxygen gas to produce iron Iron reacts with oxygen gas to produce iron (III) oxide(III) oxide

Other symbols in an Equation

•(s) = substance is solid•(l) = substance is liquid•(g) = substance is a gas•(aq) = substance is dissolved in water

• = heat

Other symbols in an Equation

•(A formula written above or below an arrow means it is a catalyst (a substance that speeds up a reaction without being used up by it.)

What is:

• The name of something that speeds a reaction, but is not used up?

• The name of what you have before a reaction takes place?

• The symbol for heat?• The number that shows there are

more than one of the entire compound?

Types of reactions

• There are five types of reactions–Combination–Decomposition–Single replacement–Double replacement–Combustion

Combination Reaction

•A combination reaction occurs when two or more elements or compounds combine to form a single substance.

•It will follow the form A + B AB

•Example: Fe + S FeS

Decomposition Reaction

•A decomposition reaction occurs when one substance breaks down into two or more substances.

•It will follow the pattern AB A + B

•Example: CaCO3CaO+CO2

Single Replacement Reaction

• One element replaces another element in a compound.

• Generally follows the formula:AB + C A + BC

• Example: Mg+Zn(NO3)2Zn+Mg(NO3)2

Double Replacement Reaction

• The exchange of two positive ions between two reacting compounds, forming two new compounds as a product.

• Generally follows the formula:AB + CD AD + CB

• Example:Na2S+Cd(NO3)2CdS+2NaNO3

Combustion Reaction

• A compound reacts with oxygen to producing energy as heat and light.

• Most of the time, it is a hydrocarbon reacting with oxygen, and the outcome is always carbon dioxide and water

• Follows the form: A + O2 CO2 + H2O

• Example: CH4 + O2 CO2 + 2H2O

What type of reaction is:

•NaCN + H2SO4 2HCN + Na2SO4

•Zn + 2HCl ZnCl2 + H2

•2C2H6 + 7O2 4CO2 + 6H2O

•2H2 + O2 2H2O

ON THE WHITEBOARDS:

•Tell which of the five types of reactions the following are:

2Na + 2H2O 2NaOH + H2

Single replacement

Fe + S FeScombination

Al(OH)3 + 3NaCl AlCl3 + 3NaOH

Double replacement

CH4 + 2O2 CO2 + 2H2Ocombustion

KClO2 KCl + O2

decomposition

NaOH + HCl NaCl + H2ODouble replacement

4Fe + 3O2 2Fe2O3

combination

2C2H2 + 5O2 4CO2 + 2H2Ocombustion

H2 + Cl2 2HClcombination

MgO + 2KF MgF2 + K2ODouble replacement

Na + Al(NO3)3NaNO3 + AlSingle replacement

2PbO2 2PbO + 3O2

decomposition

Ba(CN)2 + H2SO4 BaSO4 + HCNDouble replacement

C3H8 + 5O2 3CO2 + 4H2Ocombustion

4Li + O2 2Li2Ocombination

2Ag + 2HCl 2AgCl + H2

Single replacement

2H2O2 2H2O + O2

decomposition

C2H2 + O2 CO2 + H2Ocombustion

2HBr H2 + Br2

decomposition

CrSO4 + 2AgNO3 Cr(NO3)2 + Ag2SO4Double replacement