Chapter 8 Chemical Reactions

8.1 What Is a Chemical Reaction? One or more substance(s) are converted into new substances. Reactants are the starting materials. Products are the newly created substances.

8.1 What Is a Chemical Reaction? Chemical equation Showing a chemical reaction Reactants are on the left. Products on the right.  means “react to form” or “Yields” Reactants  Products

8.2 Reactants Transformed into Products? Consider the reaction: H2 + I2  2HI The reactants’ chemical and physical properties change! HI is not at all like H2 or I2

8.3 Balancing Chemical Equations Balanced chemical reaction Shorthand method representing a reaction H2 + I2  HI But the number and type of atoms must be the same on both sides of an equation Obey the Law of Conservation of Matter Does this equation obey?

8.3 Balancing Chemical Equations Balancing equations Balance by placing coefficients before reactants and products: H2 + I2  HI H2 + I2  2HI Reactants: 2H and 2I 2H and 2I Products: 1H and 1I 2H and 2I

8.3 Balancing Chemical Equations What about 2H2 + 2I2  4HI? Sorry  Use smallest whole numbers as coefficients! H2 + I2  2HI

8.3 Balancing Chemical Equations One more thing: Never balance equations using subscripts! Changing the subscript changes the compound…a balancing “no-no”!

8.2 Reactants Transformed into Products? Reaction between molecules Molecules collide with enough speed and at the correct angle to break reactant bonds! Energy is absorbed (endothermic) Energy is released when those bonds reform! (exothermic)

8.4 Types of Reactions Reaction types: each of these reactions is classified based on how the reactants form the products… Single-replacement reaction Double-replacement reaction Decomposition reaction Combination reaction Combustion reaction Acid/Base reaction

8.4 Types of Reactions Single-replacement reaction An element replaces different one in a compound: The single element MUST BE more reactive than the element it replaces Al is more reactive than Fe 2 Al + Fe2O3  Al2O3 + 2 Fe Double-replacement reaction Elements replace each other in two compounds: PCl3 + 3AgF  PF3 + AgCl

Decomposition reaction 8.4 Types of Reactions Decomposition reaction One compound breaks down to two or more substances One reactant, multiple products 2HgO(s)  2Hg(l) + O2(g) Combination (aka addition/synthesis) Two or more reactants combine to give another substance. Multiple reactants, one product H2(g) + I2(g)  2 HI(g)

8.4 Types of Reactions

8.4 Types of Reactions Combustion reaction Reaction of substance with O2 “Burning” Fits into the other classes also Products are often (but not always) H2Oand CO2

Team Work Problems part 1!

8.5 Part 2: Precipitation Reactions Precipitation reaction (double replacement) Solid product forms from mixing two or more solutions The solid that forms is the precipitate: Ca(NO3)2(aq)+ 2NaF(aq)  2NaNO3(aq)+ CaF2(s) The reactant salts are both soluble in water CaF2 is INSOLUBLE in water so precipitates! PPT “drop out” because they don’t dissolve

8.5 Solubility and Precipitation Reactions Dissociation This is what happens when compounds dissolve Ionic crystal lattice breaks apart into + and - ions Covalent crystals separate into discrete molecules NaCl(aq) means the crystal dissociated into Na+(aq) and Cl-(aq) The ions are spread throughout the mixture! Dissociation Animation

8.5 Solubility and Precipitation Reactions Dissociation C6H12O6(aq) means the molecular crystal breaks into separate molecules The molecules are spread throughout the mixture! Dissociation Animation

8.5 Solubility and Precipitation Reactions Mass of a substance that dissolves in water at a particular temperature Some molecular compounds dissolve in water Polar molecules that are similar to water… HCl and NH3 are examples Most molecules are not very soluble in water Many ionic compounds dissolve in water Since they are composed if charged ions and therefore polar..but not all do! Solubility rules tell which ones are soluble!

8.5 Solubility and Precipitation Reactions ANY compound with these is soluble! PbCl2 BaSO4 NOT SOLUBLE

8.5 Solubility and Precipitation Reactions Double Replacement...is there a precipitate? Pb(NO3) 2(aq) + NaI(aq)  PbI2 + NaNO3 -Balance the equation first and find out!

8.5 Solubility and Precipitation Reactions BALANCED Equation Pb(NO3) 2(aq) + 2NaI(aq)  PbI2(s) + 2NaNO3(aq) Is either product insoluble?(check rules) NaNO3 is soluble so it stays (aq) PbI2 is Insoluble (iodide salt of lead!) PbI2 is INSOLUBLE so it precipitates…(S) This is a precipitate reaction! Lead iodide reaction

8.5 Ionic and Net Ionic Equations Full Equation Pb(NO3) 2(aq) + 2NaI(aq)  PbI2(s) + 2NaNO3(aq) Complete ionic equation… Pb2+(aq) + 2 NO3- (aq) + 2 Na+(aq) + 2 I- (aq)  PbI2(s) + 2 Na+(aq) + 2 NO3-(aq) Identify Spectator IONS and cancel out! Write the NET ionic equation with what’s left: Pb2+(aq) + 2 I- (aq)  PbI2(s) PbI2 is INSOLUBLE so it precipitates!

8.5 Solubility and Precipitation Reactions A solution of sodium sulfate is combined with a solution of barium chloride. Does a precipitate form? Follow the example and figure it out: Write equation and balance it Determine if one product is insoluble Write full ionic equation Write net ionic equation Identify the ppt.

8.5 Solubility and Precipitation Reactions A solution of sodium sulfate is combined with a solution of barium chloride. Does a precipitation reaction occur? YES: Ba2+(aq) + SO42-(aq)  BaSO4(s)

8.6 Introduction to Acid−Base Reactions Substance that dissociates H+(aq) Examples: HCl (shown below) and HF

8.6 Introduction to Acid−Base Reactions Substance that dissociates OH-(aq) Examples include NaOH, KOH, and Ca(OH)2.

8.6 Introduction to Acid−Base Reactions Acid-base neutralization Acid + Base  a salt + water HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) Net ionic equation H+(aq) + OH-(aq)  H2O(l)

8.6 Introduction to Acid−Base Reactions Determine the neutralization products of the reaction between chlorous acid and sodium hydroxide… Balance full equation Write full and net ionic equations

8.6 Introduction to Acid−Base Reactions Determine the neutralization products of the reaction between chlorous acid and sodium hydroxide… Balance full equation Write full and net ionic equations HClO2(aq) + NaOH(aq)  NaClO2 (aq) + H2O(l) Net ionic equation H+(aq) + OH-(aq)  H2O(l)