Chapter 8 Notes, Part I Parts of an equation Types of reactions

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

A Chemical Equation A chemical equation shows what is going on in a chemical reaction.A chemical equation shows what is going on in a chemical reaction. Instead of writing down the entire sentence “hydrogen reacts with oxygen to form dihydrogen monoxide (water)”, you could write…Instead of writing down the entire sentence “hydrogen reacts with oxygen to form dihydrogen monoxide (water)”, you could write…

2H 2 + O 2  2H 2 Oreactantsproducts The substances you have before a chemical reaction occurs The substances you have after a chemical reaction occurs (found on the left side of the equation) (found on the right side of the equation)

2H 2 + O 2  2H 2 Osubscriptscoefficients How many elements are in a compound How many substances are in the reaction

2H 2 + O 2  2H 2 O The arrow reads as “produces”, “yields” or “reacts to form”

4Fe + 3O 2  2Fe 2 O 3 Iron reacts with oxygen gas to produce iron (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: CaCO 3  CaO+CO 2

Single Replacement Reaction One element replaces another element in a compound. Generally follows the formula: AB + C  A + BC Example: Mg+Zn(NO 3 ) 2  Zn+Mg(NO 3 ) 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: Na 2 S+Cd(NO 3 ) 2  CdS+2NaNO 3

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 + O 2  CO 2 + H 2 O Example: CH 4 + O 2  CO 2 + 2H 2 O

What type of reaction is: NaCN + H 2 SO 4  2HCN + Na 2 SO 4 Zn + 2HCl  ZnCl 2 + H 2 2C 2 H 6 + 7O 2  4CO 2 + 6H 2 O 2H 2 + O 2  2H 2 O

ON THE WHITEBOARDS: Tell which of the five types of reactions the following are:

2Na + 2H 2 O  2NaOH + H 2 Single replacement

Fe + S  FeS combination

Al(OH) 3 + 3NaCl  AlCl 3 + 3NaOH Double replacement

CH 4 + 2O 2  CO 2 + 2H 2 O combustion

KClO 2  KCl + O 2 decomposition

NaOH + HCl  NaCl + H 2 O Double replacement

4Fe + 3O 2  2Fe 2 O 3 combination

2C 2 H 2 + 5O 2  4CO 2 + 2H 2 O combustion

H 2 + Cl 2  2HCl combination

MgO + 2KF  MgF 2 + K 2 O Double replacement

Na + Al(NO 3 ) 3  NaNO 3 + Al Single replacement

2PbO 2  2PbO + 3O 2 decomposition

Ba(CN) 2 + H 2 SO 4  BaSO 4 + HCN Double replacement

C 3 H 8 + 5O 2  3CO 2 + 4H 2 O combustion

4Li + O 2  2Li 2 O combination

2Ag + 2HCl  2AgCl + H 2 Single replacement

2H 2 O 2  2H 2 O + O 2 decomposition

C 2 H 2 + O 2  CO 2 + H 2 O combustion

2HBr  H 2 + Br 2 decomposition

CrSO 4 + 2AgNO 3  Cr(NO 3 ) 2 + Ag 2 SO 4 Double replacement