2Chapter Outline 8.1 The Chemical Equation 8.4 Types of Chemical Equations8.2 Writing and Balancing Equations8.5 Heat in Chemical Reactions8.3 What Information Does an Equation Tell Us
3Chemical equations provide us with the means to Chemists use chemical equations to describe reactions they observe in the laboratory or in nature.Chemical equations provide us with the means tosummarize the reactiondisplay the substances that are reactingshow the productsindicate the amounts of all component substances in a reaction.
5Chemical reactions always involve change. Atoms, molecules or ions rearrange to form new substances.The substances entering the reaction are called reactants.The substances formed in the reaction are called products.During reactions, chemical bonds are broken and new bonds are formed.
6A chemical equation is a shorthand expression for a chemical change or reaction. A chemical equation uses the chemical symbols and formulas of the reactants and products and other symbolic terms to represent a chemical reaction.
7Coefficients (whole numbers) are placed in front of substances to balance the equation and to indicate the number of units (atoms, molecules, moles, or ions) of each substance that are reacting.
11The physical state of a substance is indicated by symbols such as (l) for liquid.
122Al(s) + Fe2O3(s) 2Fe(l) + Al2O3 (s) (s) (l) In a chemical reaction atoms are neither created nor destroyed.2Al(s) + Fe2O3(s) 2Fe(l) + Al2O3 (s)(s)(l)All atoms present in the reactant must also be present in the products.
20Never change a correct formula to balance an equation. To balance an equation adjust the number of atoms of each element so that they are the same on each side of the equation.Never change a correct formula to balance an equation.
22mercury(II) oxide → mercury + oxygen Step 1 Identify the reaction. Write a description or word equation for the reaction.Mercury (II) oxide decomposes to form mercury and oxygen.mercury(II) oxide → mercury + oxygen
23The formulas of the reactants and products can never be changed. Step 2 Write the unbalanced (skeleton) equation.The formulas of the reactants and products must be correct.The reactants are written to the left of the arrow and the products to the right of the arrow.HgO Hg + O2The formulas of the reactants and products can never be changed.
24Element Reactant Side Product Side Step 3a Balance the equation.HgO → Hg + O2Element Reactant Side Product SideHgThere is one mercury atom on the reactant side and one mercury atom on the product side.Mercury is balanced.
25Step 3a Balance the equation. Count and compare the number of atoms of each element on both sides of the equation.Determine the elements that require balancing.
26Element Reactant Side Product Side Step 3a Balance the equation.HgO Hg + O2Element Reactant Side Product SideOThere are two oxygen atoms on the product side and there is one oxygen atom on the reactant side.Oxygen needs to be balanced.
27Step 3b Balance the equation. Balance each element one at a time, by placing whole numbers (coefficients) in front of the formulas containing the unbalanced element.A coefficient placed before a formula multiplies every atom in the formula by that coefficient.
28Element Reactant Side Product Side Step 3b Balance the equation.HgO Hg + O22Element Reactant Side Product SideOPlace a 2 in front of HgO to balance O.There are two oxygen atoms on the reactant side and there are two oxygen atoms on the product side.Oxygen (O) is balanced.
29Step 3c Balance the equation. Check all other elements after each individual element is balanced to see whether, in balancing one element, another element became unbalanced.
30Element Reactant Side Product Side Step 3c Balance the equation.2HgO Hg + O2Element Reactant Side Product SideHgCount and compare the number of mercury (Hg) atoms on both sides of the equation.There are two mercury atoms on the reactant side and there is one mercury atom on the product side.Mercury (Hg) is not balanced.
31Element Reactant Side Product Side Step 3c Balance the equation.2HgO Hg + O22Element Reactant Side Product SideHgPlace a 2 in front of Hg to balance mercury.There are two mercury atoms on the reactant side and there are two mercury atoms on the product side.Mercury (Hg) is balanced.
32Element Reactant Side Product Side THE EQUATION IS BALANCED2HgO 2Hg + O2Element Reactant Side Product SideHgO
33sulfuric acid + sodium hydroxide → sodium sulfate + water Balance the Equationsulfuric acid + sodium hydroxide → sodium sulfate + water
34H2SO4(aq) + NaOH(aq) → Na2SO4(aq) + H2O(l) Balance the EquationH2SO4(aq) + NaOH(aq) → Na2SO4(aq) + H2O(l)2Reactant Side Product SideSO4 1 1Na 1 2O 1 1H 3 2224Place a 2 in front of NaOH to balance Na.There is one Na on the reactant side and there are two Na on the product side.
35 THE EQUATION IS BALANCED H2SO4(aq) + NaOH(aq) → Na2SO4(aq) + H2O(l)22Reactant Side Product SideSO4 1 1Na 2 2O 2 1H 4 224Place a 2 in front of H2O to balance H.There are 4 H on the reactant side and two H on the product side.
36butane + oxygen → carbon dioxide + water Balance the Equationbutane + oxygen → carbon dioxide + water
37 THE EQUATION IS BALANCED C4H10 (g) + O2 (g) → CO2(g) + H2O(l)281013Reactant Side Product SideC 8 8H 20 20O26Place a 13 in front of O2 to balance O.There are now 26 O on the product side.
62Metals K Ca Na Mg Al Zn Fe Ni Sn Pb H Cu Ag Hg An atom of an element in the activity series will displace an atom of an element below it from one of its compounds .Metals K Ca Na Mg Al Zn Fe Ni Sn Pb H Cu Ag HgSodium (Na) will displace an atom below it from one of its compounds.increasing activity
63Mg(s) + PbS(s) MgS(s) + Pb(s) Metal Higher in Activity Series Displacing Metal Below ItMg(s) + PbS(s) MgS(s) + Pb(s)Metals Mg Al Zn Fe Ni Sn PbMagnesium is above lead in the activity series.
64Ag(s) + CuCl2(s) no reaction Metal Lower in Activity Cannot Displace Metal Above ItAg(s) + CuCl2(s) no reactionMetals Pb H Cu Ag HgSilver is below copper in the activity series.
66Cl2(g) + CaBr2(s) CaCl2(aq) + Br2(aq) Halogen Higher in Activity Series Displaces Halogen Below ItCl2(g) + CaBr2(s) CaCl2(aq) + Br2(aq)Halogens F2 Cl2 Br2 I2Chlorine is above bromine in the activity series.
67AB + CD AD + CB A displaces C and combines with D The reaction can be thought of as an exchange of positive and negative groups.Two compounds exchange partners with each other to produce two different compounds.B displaces D and combines with CAB + CD AD + CB
68The Following Accompany Double Displacement Reactions formation of a precipitaterelease of gas bubblesrelease of heatformation of water
69Acid Base Neutralization acid + base → salt + waterHCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l)
70Formation of an Insoluble Precipitate AgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)Pb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)
72indirect gas formation Formation of a GasH2SO4(aq) + 2NaCN(aq) Na2SO4(aq) + 2HCN(g)NH4Cl(aq) + NaOH(aq) NaCl(aq) + NH4OH(aq)indirect gas formationNH4OH(aq) NH3(g) + H2O(l)
73Introduction to Stoichiometry: The Mole-Ratio Method
74Stoichiometry: The area of chemistry that deals with the quantitative relationships between reactants and products.Mole Ratio: a ratio between the moles of any two substances involved in a chemical reaction.The coefficients used in mole ratio expressions are derived from the coefficients used in the balanced equation.
77The mole ratio is used to convert the number of moles of one substance to the corresponding number of moles of another substance in a stoichiometry problem.The mole ratio is used in the solution of every type of stoichiometry problem.
78Step 1 Determine the number of moles of starting substance. Identify the starting substance from the data given in the problem statement. Convert the quantity of the starting substance to moles, if it is not already in moles.
79Step 2 Determine the mole ratio of the desired substance to the starting substance. The number of moles of each substance in the balanced equation is indicated by the coefficient in front of each substance. Use these coefficients to set up the mole ratio.
80Step 2 Determine the mole ratio of the desired substance to the starting substance. Multiply the number of moles of starting substance (from Step 1) by the mole ratio to obtain the number of moles of desired substance.
81Step 3. Calculate the desired substance in the units specified in the problem. If the answer is to be in moles, the calculation is completeIf units other than moles are wanted, multiply the moles of the desired substance (from Step 2) by the appropriate factor to convert moles to the units required.
82Step 3. Calculate the desired substance in the units specified in the problem.
83Step 3. Calculate the desired substance in the units specified in the problem.
84Step 3. Calculate the desired substance in the units specified in the problem.
86The limiting reactant limits the amount of product that can be formed. The limiting reactant is one of the reactants in a chemical reaction.It is called the limiting reactant because the amount of it present is insufficient to react with the amounts of other reactants that are present.The limiting reactant limits the amount of product that can be formed.
88Calculate the amount of product (moles or grams, as needed) formed from each reactant. Determine which reactant is limiting. (The reactant that gives the least amount of product is the limiting reactant; the other reactant is in excess.Calculate the amount of the other reactant required to react with the limiting reactant, then subtract this amount from the starting quantity of the reactant. This gives the amount of the that substance that remains unreacted.
90The quantities of products calculated from equations represent the maximum yield (100%) of product according to the reaction represented by the equation.
91Many reactions fail to give a 100% yield of product. This occurs because of side reactions and the fact that many reactions are reversible.
92The theoretical yield of a reaction is the calculated amount of product that can be obtained from a given amount of reactant.The actual yield is the amount of product finally obtained from a given amount of reactant.
93The percent yield of a reaction is the ratio of the actual yield to the theoretical yield multiplied by 100.