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Chapter 10.1 Chemical Equations Chemical Reaction • Process by which one or more substances are changed into new substances • Evidenced by changes in: temperature, color, odor, gas bubbles, precipitates, etc. Chemical Equation Represents a chemical reaction and relative amounts Correct equation tells us: 1. What changed – Reactants 2. What’s produced – Products 3. How much of each is involved 4. Physical state of each substance Types of Equations 1. Word Equations – sentence that describes equation Gaseous hydrogen combined with gaseous oxygen produces liquid water. Types of Equations 2. Skeleton Equations – Uses chemical formulas instead of words Practice Problems (p.279) 1. H2(g) + Br2 (g) HBr (g) 2. CO (g) + O2 (g) CO2 (g) 3. KClO3 (s) KCl (s) + O2 (g) Balanced Chemical Equation • A chemical equation that has the same number of atoms, of each element, on both sides of the equation • Requirement of the Law of Conservation of Mass • Flow Chart on page 283 Balancing Equations 1.Describe the reaction, putting reactants on the left and products on the right 2.Write the equation using symbols and formulas 3.Check for Balance using lowest possible ratio 4.Adjust coefficients to get equal numbers of each type of atom Helpful Hints 1. Never touch subscripts when balancing equations.That will change the composition and therefore the substance itself. 2. Check to be sure that you have included all sources of a particular element that you are balancing on a particular side. There may be two or more compounds that contain the same element on a given side of an equation. Helpful Hints 3. Adjust the coefficient of lone elements near the end of the balancing act since any change in their coefficient will not affect the balance of other elements 4. Diatomic elements (H,N,O, & Group 17) always appear as 2 atoms i.e O2 Chapter 10.2 Types of Reactions Single Replacement One element displaces another element E+CE+C A + BC B + AC Mg + 2 H2O Mg(OH)2 + H2 Single Replacement 1. A metal will not always replace another metal in an aqueous compound 2. Metal must be more reactive than the metal it replaces (Fig. 10.10 p.288) 3. NR indicates no reaction takes place 4. Halogens only replace elements below them on the periodic table Double Replacement One element replaces the like charged element in a compound C+CC+C AB + CD AD + CB Pb(NO3)2 + 2 KI PbI2 + 2 KNO3 Always produce a precipitate, gas, and/or water Decomposition • Breaking a compound into its component parts • Energy must be added C E+E AB A + B 2 H2O 2 H2 + O2 Decomposition Compounds break down as follows: 1. Binary Compound 2 elements 2. Acids Acidic Oxide + Water 3. Metallic Hydroxide Metallic Oxide + Water 4. Metallic Carbonate Metallic Oxide + Carbon Dioxide Decomposition 5. Metallic Chlorate Metallic Chloride + Oxygen 6. Metallic Oxides Metal + Oxygen Synthesis Two or more substances combine to form a new substance E+EC A + B AB 8 Fe + S8 8 FeS Not a practical method for creating compounds Combustion Compounds formed by burning • Oxygen is always involved CxHy + O2 CO2 + H2O C3H8 + 5O2 3CO2 + 4H2O • Release energy as heat and light