Chemical Reactions

Chemical Reaction the process by which one or more substances are changed into one or more different substances

REACTANTS the starting substances in a chemical reaction (the stuff on the left)

PRODUCTS the final substances in a chemical reaction (the stuff on the right)

General Formula for Reactions A + B  C Reactants yields Products

Law of Conservation of Mass/Matter Mass/Matter can not be created nor destroyed, simply changed from 1 form to another

EQUATIONS CH4 + 2O2 CO2 + 2H2O

REPRESENTATION OF PHYSICAL STATES IN EQUATIONS You may see these in book problems (g) = gas (l) = liquid (cr) = solid (stands for crystalline) (aq) = substance dissolved in water

WRITING BALANCED EQUATIONS STEP 1: Write all of the atoms in the reactants and the products (in the same order) STEP 2: Put * next to the atom in step 1, if an element occurs more than once on one side of a reaction STEP 3: Balance the equation (get the same # of atoms of each element on each side). You can only do this by changing coefficients!

WARNING!!! Never Ever CHANGE THE SUBSCRIPT

Hints for Balancing Balance metals first Then balance polyatomics Then balance non-metals Last, balance hydrogens

Hints for Balancing If an element is by itself, balance it last Watch for even or odds, balance accordingly Don’t forget your diatomics in transcribed problems Don’t forget to Kriss Kross and use ( )

Hints for Balancing 1st, balance anything that is found in 1 product/reactant Then, balance anything that is found in 2 or more products / reactants

Reaction of Zinc with HCl Please balance the equation __Zn + __HCl à __ZnCl2 + __H2 Zn = 1 H = 1 Cl = 1 Zn = 1 H = 2 Cl = 2

Combustion of ethane C2H6 Please balance the equation __C2H6 + __O2 à __CO2 + __H2O C = 2 H = 6 O = 2 C = 1 H = 2 *O = 3

Zinc + Hydrochloric Acid Please write the reaction

Writing Balanced Equations When Given Words Only STEP 1: Write out the symbols STEP 2: Balance your charges (if needed) STEP 3: Check for diatomics STEP 4: Balance Equation

Hints for Balancing Don’t forget your diatomics in transcribed problems Don’t forget to Kriss Kross and use ( )

Combustion of Acetone (CH3)2CO Please write the reaction (CH3)2CO(l) + O2(g) à CO2(g) + H2O(g)

HOMEWORK Pg. 228 #1-12 Pg. 243 #43, 45, 46, 58 Worksheet

two or more substances combine to form one new substance SYNTHESIS two or more substances combine to form one new substance

SYNTHESIS A + B  AB Na + Cl2  NaCl Pb(IV) + O2  Pb2O4

Info on Synthesis Reactions Also known as “combination” reactions Always form compounds Generally give off lots of energy Can be reversed (decomposition)

when a substance breaks up into simpler substances DECOMPOSITION when a substance breaks up into simpler substances

Decomposition AB  A + B NaCl  Na + Cl2 Pb2O4  Pb + O2

Info on Decomp Reactions Energy is usually need to make these reactions happen Often hard to predict products unless the substance breaks into its ionic components (or memorize some basic types of reactions) Often are the cause of explosions

Types Decomp Reactions Metallic Carbonates When heated, metallic carbonates decompose into metallic oxides and carbon dioxide BaCO3 --> BaO + CO2 Cu2CO3 --> Cu2O + CO2

Types Decomp Reactions Metallic Chlorates When heated, metallic chlorates decompose into metallic chlorides and oxygen KClO3 --> KCl + O2 Zn(ClO4)2 --> ZnO + O2

Types Decomp Reactions Metallic Hydroxides When heated, metallic hydroxides decompose into metallic oxides and water Ca(OH)2 --> CaO + H2O Mn(OH)4 --> Mn2O4 + H2O

Types Decomp Reactions Metallic Oxides When heated, metallic oxides decompose into the metal and oxygen K2O --> K + O2 Pb2O4 --> Pb + O2

Decomp of Trinitrotoluene 2C7H5N3O6 (s) --> 3N2(g) + 7CO2(g) + 5H2O(g) + 7C(s) 2 moles of TNT decompose to produce 15 moles of hot, expanding gases…that is why it is so powerful!

one element displaces another in a compound SINGLE DISPLACEMENT one element displaces another in a compound

Single Displacement Reaction

AB + C  AC + B or CB + A Single Displacement NaBr + Cl2  NaCl + Br2 (NH4)2S + O2  (NH4)2O + S

Info on Single Replacement Also known as single displacement reactions Only elements with a higher activity can replace other elements (use table on pg. 217) Nonmetals can replace other non-metals, but is usually limited to halogens (active decreases down table)

Types Single Replacement Metals More active metal atoms will replace less active metal ions from compounds Cu + AgNO3 --> Ag + Cu(NO3)2 Ag + Cu(NO3) --> No Reaction

Types Single Replacement Halogens More active halogen atoms will replace less active halogen ions from compounds F2 + NaCl --> Cl2 + NaF Cl2 + FCl --> No Reaction

Types Single Replacement Halogens More active halogen atoms will replace less active halogen ions from compounds F2 + NaCl --> Cl2 + NaF Cl2 + FCl --> No Reaction

negative portions of two compounds are switched DOUBLE DISPLACEMENT the positive or negative portions of two compounds are switched

Double Displacement AB + CD  AD + CB NaBr + Pb2S3  Na2S + PbBr3 K2SO4 + Ba(OH)2 KOH + BaSO4

Info on Double Replacement Also known as double displacement reactions Reactants must be two ionic compounds in aqueous solution Cations switch positions Usually produces a precipitate (ppt)

For Double Replacement to Occur one is Usually True Also known as double displacement reactions Reactants must be two ionic compounds in aqueous solution Cations switch positions Usually produces a precipitate (ppt)

hydrocarbon reacts with oxygen to form carbon dioxide and water COMBUSTION (aka OXIDATION) hydrocarbon reacts with oxygen to form carbon dioxide and water

Writing Out Equations STEP 1: Determine type of rxn STEP 2: Write out symbols STEP 3: Kriss-Kross where necessary STEP 4: Diatomics STEP 5: Balance the equation

Common Words Decomposes = breaks apart Combusts = a combustion rxn Reacts with = A + B “To form” or “to get”=  Yields =  Displaces = have a single D. rxn And = plus (+)

Common Words Decomposes = breaks apart Combusts = a combustion rxn Reacts with = A + B “To form” or “to get”=  Yields =  Displaces = have a single D. rxn And = plus (+)

HOMEWORK Pg. 231 #13-22