C HEMICAL R EACTIONS Chemistry Matter and Change Chapter 9

Chapter 9 Big Idea Millions of chemical reactions in and around you transform reactants into products, resulting in the absorption or release of energy.

R EACTIONS AND E QUATIONS Chemistry Matter and Change Chapter 9.1

9.1 Main Idea Chemical reactions are represented by balanced chemical equations.

9.1 Objectives Recognize evidence of chemical reactions Represent chemical reactions with equations Balance chemical equations

9.1 Review Vocabulary and Concepts Chemical change Dalton’s atomic theory Law of conservation of mass

9.1 New Vocabulary and Concepts Chemical reaction Reactant Product Chemical equation Coefficient (s), (l), (g), (aq)  

Chemical reaction Process by which atoms are rearranged

Evidence of chemical reactions Temperature/energy change Gas emitted (odor) Precipitate forms Color change Change of substance(s)

Representing chemical reactions 4+1=2+3 Reactant + reactant  product + product Need one or more reactants and one or more products

Symbols you need to know SymbolMeaning +Plus  Yields  Reversible reaction (s)Solid (l)Liquid (g)Gas (aq)Aqueous (in water) χ represents something that is needed for the reaction, but not consumed in the reaction

Three types of equations Word equations Skeletal equations Chemical equations

Types of equations Skeletal Indicates identity (by molecular formulae) of substances involved Chemical Indicates identity (by molecular formulae) and relative quantity of substances involved Word Indicates identity of substances involved Hydrogen + oxygen  water H 2 + O 2  H 2 O2H 2 + O 2  2H 2 O

Balancing chemical equations Conservation of mass –What goes in, must come out –What comes out, must have gone in

Balancing equations: 1.Write out word equation 2.Write out skeletal equation 3.Balance each atom –MINOH (aka Tarzan method) Metals, ions, nonmetals, oxygen, hydrogen –Start with “rare” elements –Leave atoms in multiple places until last “Me know chemistry,” said Tarzan as he climbed the stoichiom-eh-tree.

Sample 1 Magnesium and bromine form magnesium bromide –Mg + Br 2  MgBr 2 (balanced) Magnesium and oxygen form magnesium oxide –Mg + O 2  MgO (not balanced) –2Mg + O 2  2MgO (balanced)

Sample 2 Nitrogen and hydrogen form ammonia N 2 + H 2  NH 3 N 2 + 3H 2  2NH 3

Sample 3 Zn + HCl  ZnCl 2 + H 2 Na + H 2 O  NaOH + H 2

For you to practice Fe + O 2  Fe 2 O 3 Fe 2 O 3 + H 2  Fe + H 2 O Sb + O 2  Sb 4 O 6 Al + HCl  AlCl 3 + H 2 H 2 O + CO 2  C 6 H 12 O 6 + O 2

More hints Keep polyatomic ions together if they appear on both sides of the equation Diatomics always exist in pairs

Can you… Recognize evidence of chemical reactions Represent chemical reactions with equations Balance chemical equations

C LASSIFYING C HEMICAL R EACTIONS Chapter 9.2

9.2 Main Idea There are five types of chemical reactions: synthesis, decomposition, single replacement, double replacement, and combustion

9.2 Objectives Classify chemical reactions Identify the characteristics of different classes of chemical reactions

9.2 Review Vocabulary and Concepts Metal Nonmetal precipitate

9.2 New Vocabulary and Concepts Synthesis reaction Combustion reaction Decomposition reaction Single-replacement reaction Double replacement reaction

5 Types of chemical reactions 1.Synthesis 2.Decomposition 3.Combustion 4.Single replacement (displacement) 5.Double replacement (displacement)

Synthesis E+E  C Two or more reactants form one product 2H 2 + O 2  2H 2 O + 

Decomposition C  E+E One reactant breaks down into two or more products 2Fe 2 O 3  4Fe + 3O 2  +

Single replacement C + E  E + C One element in a compound is replaced by another element Br 2 + MgCl 2  MgBr 2 + Cl 2  + +

Double replacement C+C  C+C Elements in both compounds change partners Ca(OH) 2 +2HCl  CaCl 2 +2H 2 O  ++

Combustion C + O 2  CO 2 + H 2 O A compound plus oxygen produces an oxide and water 2C 2 H 6 + 7O 2  4CO 2 + 6H 2 0

Summary of reaction types Reaction TypeReactantsProbably ProductsGeneric Equation SynthesisTwo or more substances One compoundA+B  AB DecompositionOne compoundTwo or more substances AB  A+B Single replacementA metal and a compound A nonmetal and a compound A new metal and compound A new nonmetal and a compound A+BX  AX+B Double replacementA metal and a compound A new compound and metal AX+BY  AY+BX CombustionCompound and oxygen An oxideA+O 2  AO

Predict the product(s) NaOH+HCl  CH 4 +O 2  LiCl+Br 2  Fe+O 2  H 2 O 

Can you… Classify chemical reactions Identify the characteristics of different classes of chemical reactions

R EACTIONS IN A QUEOUS S OLUTIONS 9.3

9.3 Main Idea Double replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or gases.

9.3 Objectives Describe aqueous solutions Write complete ionic and net ionic equations for chemical reactions in aqueous solutions Predict whether reactions in aqueous solutions will produce a precipitate, water or a gas

9.3 Review Vocabulary and Concepts Solution Ionic formulae Precipitate Ion

9.3 New Vocabulary and Concepts Aqueous solution Solute Solvent Complete ionic equation Spectator ion Net ionic equation

Aqueous solutions Solvent- water Solute- other substance(s) –HCl (aq) is hydrochloric acid in water

Types of reactions in aqueous solutions Form Gas –Usually Double displacement

Types of reactions in aqueous solutions Form Precipitate –Usually double replacement 2KI + Pb(NO 3 ) 2  2KNO 3 +PbI 2 Lead iodide

Types of reactions in aqueous solutions Form Water –Acid/base reactions Double displacement –Also form a salt HCl + NaOH  NaCl+ HOH

Net Ionic Reactions Allow you to predict the products in a double replacement reaction HBr (aq) +NaOH (aq)  H 2 O (l) +NaBr (aq) H + (aq) + Br - (aq) + Na + (aq) + OH - (aq)  H 2 O (l) + Na + (aq)+ Br - (aq) H + + OH -  H 2 O

Writing Net Ionic Reactions Perchloric acid reacts with aqueous potassium carbonate forming potassium chlorate, carbon dioxide gas and water. Step 1: figure out the chemical formulae and phase for all substances Perchloric acid: HClO 4(aq) Potassium carbonate: K 2 CO 3(aq) Water: H 2 O (l) Carbon dioxide: CO 2(g) Potassium perchlorate : KClO 4

Writing Net Ionic Reactions Perchloric acid reacts with aqueous potassium carbonate forming potassium chlorate, carbon dioxide gas and water. Step 2: write the skeletal equation HClO 4(aq) +K 2 CO 3(aq)  H 2 O (l) +CO 2(g) +KClO 4(aq)

Writing Net Ionic Reactions Perchloric acid reacts with aqueous potassium carbonate forming potassium chlorate, carbon dioxide gas and water. Step 3: balance the equation 2HClO 4(aq) + K 2 CO 3(aq)  H 2 O (l) +CO 2(g) + 2KClO 4(aq)

Writing Net Ionic Reactions Perchloric acid reacts with aqueous potassium carbonate forming carbon dioxide gas and water. Step 4: Write the complete ionic equation 2H + (aq) + 2ClO 4 - (aq) + 2K + (aq) + CO 3 2- (aq)  H 2 O (l) + CO 2(g) + 2K + (aq) + 2ClO 4 - (aq)

Writing Net Ionic Reactions Perchloric acid reacts with aqueous potassium carbonate forming carbon dioxide gas and water. Step 5: Cross out balanced terms 2H + (aq) + 2ClO 4 - (aq) + 2K + (aq) + CO 3 2- (aq)  H 2 O (l) + CO 2(g) + 2K + (aq) + 2ClO 4 - (aq)

Writing Net Ionic Reactions Perchloric acid reacts with aqueous potassium carbonate forming carbon dioxide gas and water. Step 6: write net ionic equation 2H + (aq) + CO 3 2- (aq)  H 2 O (l) +CO 2(g)

Practice Sulfuric acid reacts with aqueous sodium cyanide, forming hydrogen cyanide gas and aqueous sodium sulfate –You can reduce coefficients if you’d like 2H + (aq) + 2CN - (aq)  2HCN (g) or H + (aq) + CN - (aq)  HCN (g)

Can you… Describe aqueous solutions Write complete ionic and net ionic equations for chemical reactions in aqueous solutions Predict whether reactions in aqueous solutions will produce a precipitate, water or a gas