6 2H2(g) + O2(g) 2H2O(g) D. Writing Equations How many? - coefficient Identify the substances involved.Use symbols to show:How many? - coefficientOf what? - chemical formulaIn what state? - physical stateRemember the diatomic elements.
7 D. Writing Equations 2 Al (s) + 3 CuCl2 (aq) 3 Cu (s) + 2 AlCl3 (aq) Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride.How many?Of what?In what state?2Al(s)+ 3CuCl2(aq) 3Cu(s)+ 2AlCl3(aq)
8 E. Describing Equations Describing Coefficients:individual atom = “atom”covalent substance = “molecule”ionic substance = “unit”3CO2 2Mg 4MgO 3 molecules of carbon dioxide2 atoms of magnesium4 units of magnesium oxide
9 E. Describing Equations Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)How many?Of what?In what state?One atom of solid zincreacts withtwo molecules of aqueous hydrochloric acidto produceone unitof aqueous zinc chlorideand onemolecule of hydrogen gas.
10 F. Chemical vs. Physical (revisited) Chemical changes – make something newEx: sodium and chlorine react to make table saltPhysical changes – just change the physical nature of the substance (the chemical formula remains the same)Ex: Ice melts into liquid water (formula remains H2O)
11 II. Balancing Equations 9.1 - continuedII. Balancing Equations
12 A. Balancing Steps1. Write the unbalanced equation. 2. Count atoms on each side. 3. Add coefficients to make #s equal. Coefficient subscript = # of atoms 4. Reduce coefficients to lowest possible ratio, if necessary. 5. Double check atom balance!!!
13 B. Helpful Tips Balance one element at a time. Update ALL atom counts after adding a coefficient.If an element appears more than once per side, balance it last.Balance polyatomic ions as single units.“1 SO4” instead of “1 S” and “4 O”
14 C. Balancing Example 2 Al + CuCl2 Cu + AlCl3 Al Cu Cl 3 3 2 2 1 1 Aluminum and copper(II) chloride react to form copper and aluminum chloride.2Al CuCl2 Cu AlCl3AlCuCl3322 2 63 6 3
15 III. Types of Chemical Reactions 9.2 – Classifying Chemical ReactionsIII. Types of Chemical Reactions
16 CH4(g) + 2O2(g) CO2(g) + 2H2O(g) A. Combustionthe burning of any substance in O2 to produce heatA + O2 BCH4(g) + 2O2(g) CO2(g) + 2H2O(g)
17 A. Combustion 4 2 Na(s)+ O2(g) Na2O(s) C3H8(g)+ O2(g) 5 3 4 Products:contain oxygenhydrocarbons form CO2 + H2ONa(s)+ O2(g) Na2O(s)C3H8(g)+ O2(g) CO2(g)+ H2O(g)
18 B. Synthesisthe combination of 2 or more substances to form a compoundonly one productA + B AB
23 C. Decomposition 2 2 KBr(l) K(s) + Br2(l) Products: binary - break into elementsDiatomics – N2, O2, F2, Cl2, Br2, I2others - hard to tellKBr(l) K(s) + Br2(l)
24 A + BC B + AC D. Single Replacement one element replaces another in a compoundmetal replaces metal (+)nonmetal replaces nonmetal (-)A + BC B + AC
25 Cu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s) D. Single ReplacementCu(s) + 2AgNO3(aq) Cu(NO3)2(aq) + 2Ag(s)
26 D. Single Replacement Fe(s)+ CuSO4(aq) Cu(s)+ FeSO4(aq) Products:Free element kicks outnonmetal nonmetal (-)free element on reactants side must be more active (check activity series)Fe(s)+ CuSO4(aq) Cu(s)+ FeSO4(aq)Br2(l)+ NaCl(aq) N.R.
27 AB + CD AD + CB E. Double Replacement ions in two compounds “change partners”cation of one compound combines with anion of the otherAB + CD AD + CB