Chap. 8: Chemical Reactions Translate word equations into balanced chemical equations. Deduce the chemical equations when all reactants and products are given. Identify types of chemical reactions. Predict products of chemical reactions given the reactants.

Deduce chemical equations when all reactants and products are given. What is a chemical reaction? Rearrangement of atoms forming new substances Reactants  Products Some reactions are desirable… Glucose + oxygen  Carbon dioxide + water …some are not. Iron + oxygen  iron (III) oxide

Deduce chemical equations when all reactants and products are given. Chemical formulas are easier and more informative to use in equations than words. A skeleton equation is a chemical equation that shows what reactants and products are involved. It does not necessarily indicate the relative amounts of reactants and products. Fe + O2  Fe2O3 Sometimes the skeleton equation is balanced (all coefficients = 1). SnO2(s)  Sn(s) + O2(g)

Deduce chemical equations when all reactants and products are given. Symbols used in chemical reactions + Used to separate two reactants or products “Yields” separates products from reactants  Used in place of  for reversible reactions (s) Designates a solid reactant or product (l) Designates a liquid reactant or product (g) Designates a gaseous reactant or product (aq) Designates an aqueous reactant or product  Indicates that heat is supplied to the reaction

Translate word equations into chemical equations. Zinc + lead(II) nitrate  zinc nitrate + lead Zn + Pb(NO3)2  Zn(NO3)2 + Pb

Translate word equations into chemical equations. Aluminum bromide + chlorine yield aluminum chloride + bromine AlBr3 + Cl2*  AlCl3 + Br2* *Note: chlorine and bromine are diatomic meaning they are written as elements containing 2 atoms. Diatomics are:H2; N2; O2; F2; Cl2; Br2; I2 GO TO HANDOUT 6A – Words into equations Do not Balance

Deduce chemical equations when all reactants and products are given. Balancing chemical equations The Law of Conservation of Matter: In a chemical (non-nuclear) reaction, atoms are neither created nor destroyed. For an equation to be balanced the number of atoms of each element is the same on both sides of the equation. H2(g) + O2(g)  H2O (l) (unbalanced) 2H2(g) + O2(g)  2H2O (l) (balanced) K(s) + H20(l)  KOH (aq) + H2(g) (unbalanced) 2K(s) + 2H20(l)  2KOH (aq) + H2(g) (balanced) C6H12O6 + O2  CO2 + H2O (unbalanced) C6H12O6 + 6O2  6CO2 + 6H2O (balanced)

Deduce chemical equations when all reactants and products are given. Rules for Balancing Equations 1) Write the correct formulas for the reactants on the left side of the yield sign and products on the right side. 2) Count the number of atoms of each element in the products and the reactants. 3) Balance the elements one at a time by using coefficients. Do not change the subscripts in the chemical formulas. 4) Check each atom or polyatomic ion to make sure the equation is balanced. 5) Make sure all coefficients are in the lowest possible ratio.

Deduce chemical equations when all reactants and products are given. Rules for Balancing Equations 1) Write the correct formulas for the reactants on the left side of the yield sign and products on the right side. 2) Count the number of atoms of each element in the products and the reactants. 3) Balance the elements one at a time by using coefficients. Do not change the subscripts in the chemical formulas. 4) Check each atom or polyatomic ion to make sure the equation is balanced. Make sure all coefficients are in the lowest possible ratio. N2 + H2  NH3 1) Formulas given 2) Reactants Products 2N 2H  1N 3H 3) Balance N by putting 2 in front of NH3 N2 + H2  2NH3 Balance H by putting 3 in front of H2 N2 + 3H2  2NH3 2N 6H  2N 6H Lowest ratio of coefficients

Deduce chemical equations when all reactants and products are given. Rules for Balancing Equations 1) Write the correct formulas for the reactants on the left side of the yield sign and products on the right side. 2) Count the number of atoms of each element in the products and the reactants. 3) Balance the elements one at a time by using coefficients. Do not change the subscripts in the chemical formulas. 4) Check each atom or polyatomic ion to make sure the equation is balanced. Make sure all coefficients are in the lowest possible ratio. KClO3  KCl + O2 1) Formulas given 2) Reactants Products 1K 1Cl 3O  1K 1Cl 2O 3) Balance O by putting 2 in front of KClO3 and 3 in front of O2 2KClO3  KCl + 3O2 Balance K & Cl by putting 2 in front of KCl 2KClO3  2KCl + 3O2 2K 2Cl 6O  2K 2Cl 6O Lowest ratio of coefficients

Translate word equations into balanced chemical equations. Zinc + lead(II) nitrate  zinc nitrate + lead 1) Zn + Pb(NO3)2  Zn(NO3)2 + Pb 2) 1Zn 1Pb 2N 6O  1Zn 1Pb 2N 6O (balanced) 3) Lowest possible ratio.

Translate word equations into balanced chemical equations. Aluminum bromide + chlorine yield aluminum chloride + bromine AlBr3 + Cl2*  AlCl3 + Br2* *Note: chlorine and bromine are diatomic meaning they are written as elements containing 2 atoms. Diatomics are:H2; N2; O2; F2; Cl2; Br2; I2 2) 1Al 3Br 2Cl  1Al 2Br 3Cl Balance Br by placing a 2 in front of AlBr3 and a 3 in front of Br2 Balance Cl by placing a 3 in front of Cl2 and a 2 in front of AlCl3 2AlBr3 + 3Cl2  2AlCl3 + 3Br2 4) 2Al 6Br 6Cl  2Al 6Br 6Cl Lowest possible ratio. STOP – Do balancing equations HO (old copy) and Go back and balance Problems, 6A. Then go to EQUATIONS HO

Identify types of chemical reactions Synthesis or Combination Reaction: Two or more substances combine to form a single substance. 2Na(s) + Cl2(g)  2NaCl(s) CaO(s) + H2O(l)  Ca(OH)2(aq) 2H2(g) + O2(g)  2H2O (l) 4Fe(s) + 3O2(g)  2Fe2O3(s) N2(g) + 3H2(g)  2NH3(g)

Identify types of chemical reactions 2) Decomposition Reactions: A single substance is broken down into two or more substances. CaCO3(s)  CaO(s) + CO2(g) 2H2O(l)  2H2(g) + O2(g) 2H2O2(aq)  2H2O(l) + O2(g)

Identify types of chemical reactions Single-Replacement Reactions: One element replaces another in a compound. Mg(s) + Zn(NO3)2(aq)  Mg(NO3)2(aq) + Zn(s) 2K(s) + 2H2O(l)  2KOH (aq) + H2(g) Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) + 2Ag(s) 2Al(s) + Fe2O3(s)  Al2O3(s) + 2Fe(s) Cl2(g) + 2NaBr(aq)  2NaCl(aq) + Br2(g)

Identify types of chemical reactions Double-Replacement Reactions: Ions of two reacting compounds trade places. Na2CO3(aq) + CaCl2(aq)  CaCO3(s) + 2NaCl(aq) Na2S(aq) + Cd(NO3)2(aq)  CdS(s) + 2NaNO3(aq) NaOH(aq) + HCl(aq)  NaCl(aq) + H2O(l) H2SO4(aq) + 2NaCN(aq)  Na2SO4(aq) + 2HCN(g)

Identify types of chemical reactions Combustion Reactions: An element or compound reacts with oxygen. Products are usually carbon dioxide and water. CH4(g) + O2(g)  CO2(g) + H2O(g) C3H8(g) + 5O2(g)  3CO2(g) + 4H2O(g) 2C8H18(l) + 25O2(g)  16CO2(g) + 18H2O(g) C2H5OH(l) + 3O2(g)  2CO2(g) + 3H2O(g) Do Handout 6b + predict the products HO