CHAPTER 7 CHEMICAL REACTIONS Problems 1 21 23 30 33 62 39 82 85 86 89 92 99 100 111 Chapter 16 Problems 77 84 111 7 2 EVIDENCE OF A CHEMICAL REACTION Evidence for Chemical Reactions a A gas is produced indicated by bubbles when two substances are mixed b A solid forms when two solutions are mixed this solid is called a precipitate c Heat energy change is noted exothermic reaction releases heat endothermic reaction absorbs heat 7 3 THE CHEMICAL EQUATION chemical equation formulas and symbols that describe a chemical reaction A B C D reactants products starting materials substances resulting from chemical reaction For example the reaction between H2 molecules in white with O2 molecules in red to make water H2O can be shown using molecular level images or with a chemical equation 2 H2 g CHEM 139 Tro Chapter 7 O2 g 2 H2O g page 1 Note that in addition to the chemical formulas the physical state of each reactant and product is indicated The physical states of all the reactants and products are also indicated s solid l liquid g gas aq aqueous ions or compounds dissolved in water coefficient Whole s in front of each reactant product indicating the number of each present subscript Whole after each element in a compound indicating of each element present GUIDELINES for Balancing a Chemical Equation 1 Count the of each element on both sides of the equation 2 Change the coefficients NEVER the subscripts to get the same of atoms of each element on both sides of the equation Balance the equation using the following order Metals Polyatomic ions Balance as a whole NOT as individual atoms Carbon Hydrogen Oxygen All other atoms Ex 1 Consider the molecular level images of the molecules below O2 CH4 CO2 H2O Balance the equation below CH4 g O2 g CO2 g H2O g Ex 2 Balance the equations below Al s N2 g O2 g Al2O3 s H2 g NH3 g NaHCO3 s Na2CO3 s H2O g CO2 g HCl aq CaCO3 s CaCl2 aq H2O l CO2 g CHEM 139 Tro Chapter 7 page 2 Treat polyatomic ions as ONE UNIT they usually do NOT break up into atoms in a reaction NO3 SO42 OH Al2 SO4 3 aq Ba NO3 2 aq BaSO4 s Al NO3 3 aq Ca NO3 2 aq K3PO4 aq Ca3 PO4 2 s KNO3 aq Sr OH 2 aq H3PO4 aq H2O l Sr3 PO4 2 s Example For each of the following descriptions i Translate each word equation into a chemical equation including physical states for all reactants and products and ii Balance the equation a Hydrogen gas and oxygen gas react to form water b sodium metal reacts with chlorine gas to produce solid sodium chloride c Zinc metal reacts with hydrochloric acid to produce hydrogen gas and aqueous zinc chloride CHEM 139 Tro Chapter 7 page 3 7 9 OXIDATION REDUCTION REDOX REACTIONS COMBINATION SYNTHESIS REACTIONS A Z AZ Two reactants combine to form one product when heated Given a metal and a nonmetal recognize they react to form a solid ionic compound Example Given a combination reaction balance the equation and classify it as a combination reaction Mg s O2 g K s Br2 s Al s S8 s MgO s KBr s Al2S3 s Note The triangle above the reaction arrow indicates that the reactants are heated to make the reaction occur COMBUSTION REACTIONS BURNING CARBON COMPOUNDS Hydrocarbons compounds with only C and H and hydrocarbon derivatives compounds with only C H and O burn in O2 to produce CO2 gas and steam H2O g CxHy O2 g CO2 g H2O g CxHyOz O2 g CO2 g H2O g xample Predict the products for the following then balance the equation 1 C3H8 g O2 g 2 C5H12 l 3 C6H6O l CHEM 139 Tro Chapter 7 O2 g O2 g page 4 DECOMPOSITION REACTIONS AZ A Z One reactant breaks down into two or more products Given an unbalanced equation for decomposition reaction balance it and classify it KClO3 s MnO 2 KCl s O2 g Al2 CO3 3 s Fe HCO3 3 s Al2O3 s CO2 g Fe2O3 s CO2 g H2O g 16 5 THE ACTIVITY SERIES PREDICTING SPONTANEOUS REDOX REACTIONS SINGLE DISPLACEMENT REACTIONS A s BX aq AX aq B ACTIVITY SERIES Relative order of elements arranged by their ability to undergo reaction Li K Ba Sr Ca Na Mg Al Mn Zn Fe Cd Co Ni Sn Pb H2 Cu Ag Au Note The Activity Series will be given to you on quizzes and exams SINGLE DISPLACEMENT REACTIONS A SOLID METAL IN A METAL SOLUTION The more active metal will go into solution aq metal A s aqueous solution B aq aqueous solution A aq metal B s Zn s Sn2 aq Sn s Zn2 aq Cu s 2 Ag aq 2 Ag s Cu2 aq CHEM 139 Tro Chapter 7 page 5 For each of the following 1 Check the Activity Series to see if the solid metal is more active If it is the reaction occurs so write the formulas for the products If it s not write NR for no reaction 2 Balance the equation if the reaction occurs 1 Zn s AgNO3 aq 2 Al s ZnCl2 aq 3 Ag s Al NO3 3 aq SINGLE DISPLACEMENT REACTIONS A METAL IN AN ACID For each of the following 1 Check the Activity Series to see if the solid metal is more active than H If not write NR for no reaction If it is the metal replaces hydrogen to form H2 g and the metal goes into solution as a cation to join the anion 2 Balance the equation if the reaction occurs metal A s acid aq aqueous solution A aq H2 g 1 Mg s HCl aq 2 Al s HBr aq 3 Cu s H2SO4 aq CHEM 139 Tro Chapter 7 page 6 SINGLE DISPLACEMENT REACTIONS ACTIVE METALS IN WATER ACTIVE METALS Li K Ba Sr Ca Na Metals that react directly with water For each of the following 1 Check to see if the solid metal is an active metal If it s not write NR for no reaction If it is the metal replaces hydrogen to form H2 g and the metal goes into solution as a cation to combine with the hydroxide anion OH 2 Balance the equation if the reaction occurs active metal s H2O l metal hydroxide aq H2 g 1 Ca s H2O l 2 K s H2O l 3 Fe s H2O l 7 5 AQUEOUS SOLUTIONS AND SOLUBILITY COMPOUNDS DISSOLVED IN WATER Some ionic compounds usually those with ions with low charges like NaCl KNO3 etc dissolve in water to form ions See the examples of KNO3 and Pb NO3 2 below CHEM 139 Tro Chapter 7 page 7 Other ionic compounds have stronger ionic bonds that cannot be broken by polar H2O molecules These ionic compounds do not dissolve in water They are insoluble in water and remain intact as solids called precipitates For example lead II iodide does not dissolves in water and remains a …