Links to diagrams and tables have been broken due to copyright laws.

Chapter 8
Chemical Equations and Reactions

1. Describing Chemical Reactions
   
   1. Introduction
      
      1. chemical reaction - definition
         
      2. reactant - definition
         
      3. product - definition
         
      4. Law of Conservation of Mass - statement
         
      5. chemical equation - definition
         e.g.
         (NH₄)₂Cr₂O₇ -----> N₂ + Cr₂O₃ + 4H₂O
         
      6. figure 8-1 page 241
         
         
   2. Indications of a Chemical Reaction
      
      1. evidence that a chemical reaction has occurred
         
      2. analysis of the product is definitive proof
         
      3. Various indications
         
         1. evolution of heat and light -- can also indicate physical change
            
         2. production of a gas e.g. baking soda + vinegar (acetic acid)
            
            1. figure 8-2a page 242
               
         3. formation of a precipitate - occurs when two solutions are mixed (e.g. solid dissolved in a liquid is one type of solution)
            
            1. precipitate - definition
               
               
   3. Characteristics of a Chemical Equation
      
      1. a chemical reaction summarizes a chemical change
         
      2. things to keep in mind about equations
         
         1. the equation must represent the known facts
            
         2. the equation must contain the correct formulas for the reactants and products
            
            1. diatomic molecules
               
            2. table 8-1 page 243
               
            3. sulfur -- S₈
               
            4. phosphorus -- P₄
               
         3. the law of conservation of mass must be satisfied
            
            1. coefficients must be used to balance the equation
               
            2. coefficient - definition
               
            3. if no coefficient - one is understood
               
      3. Word and Formula Equations
         
         1. need to represent the facts
            
         2. word equation - definition
            
         3. word equation is qualitative
            
         4. e.g. methane + oxygen ----> carbon dioxide + water
            
         5. figure 8-3a page 245
            
            1. meaning of ---->
               
         6. replace names of reactants and products with correct symbols and formulas
            
         7. formula equation - definition
            
         8. physical states in parentheses
            
            1. gas, solid, liquid, aqueous solution
               
         9. balance the equation by adding appropriate coefficients
            
            1. H₂O v 2H₂O
               
            2. figure 8-3b page 245
               
               
      4. Additional Symbols Used in Chemical Equations
         
         1. upward arrow after a substance
            
         2. downward arrow after a substance
            
         3. heat as the Greek letter D, above the arrow
            
         4. pressure value above the arrow
            
         5. temperature value above the arrow
            
         6. a chemical symbol/formula above the arrow
            
            1. catalyst - definition
               
         7. two opposing arrows -- sometimes written as an equal sign
            
            1. reversible reaction - definition
               
         8. table 8-2 page 246
            
      5. Sample Problem 8-1 page 247
         
         1. solid sodium oxide + water yields sodium hydroxide solution
            
            1. given the word equation
               
            2. write the symbol and charge for each element/ion
               
            3. balance the charges so compounds are neutral
               
            4. add subscripts to indicate physical state of each substance, if applicable
               
            5. balance the chemical equation
            
            Homework: Chapter 8, 8.1
            
            
   4. Significance of a Chemical Equation
      
      1. arrow is like equal sign i.e. equal amounts of reactants and products
         
      2. coefficients indicate relative, not absolute amounts of reactants and products i.e. coefficients are usually the smallest whole number ratio
         
      3. to get larger amounts we multiply EACH coefficient by some factor such as 2 or 3 or 4
         
      4. relative masses can be determined from the coefficients, by converting moles into grams
         
         1. figure 8-4 page 249
            
      5. the reverse reaction has the same relative amount of substances as the forward reaction
         
      6. just because we can write an equation does not mean the reaction will happen
         
      7. the chemical equation does not tell us anything about the speed at which it will occur.
         
         Homework: Chapter 8, 8.2
         
         
   5. Balancing Chemical Equations
      
      1. sequence to follow is on page 251
         
         1. balance the following
            
            1. H₂ + O₂ ---> H₂O
               
            2. PbCl₂ + Na₂CrO₄ ---> PbCrO₄ + NaCl
               
               Homework: Chapter 8, 8.3
               
               
   6. Types of Chemical Reactions
      
      1. Introduction
         
         1. Need to predict what the products of a chemical reaction will be
            
         2. either memorize all reactions or classify they into groups with predictable products
            
         3. five type of reactions: synthesis, decomposition, single replacement, double replacement, and combustion
         4. Outline of type of chemical reactions
            
            
      2. Synthesis Reactions
         
         1. synthesis reaction - definition
            
         2. aka composition reaction
            
         3. generalized equation: A + X ---> AX
            
         4. A and X can be elements or compounds
            
            1. Reactions of Elements with Oxygen and Sulfur
               
               1. element + oxygen ---> oxide
                  e.g. magnesium + oxygen ---> magnesium oxide Mg + O₂ ---> MgO
                  2Mg + O₂ ---> 2MgO
                  
               2. e.g. lithium + oxygen ---> lithium oxide
                  Li + O₂ ---> Li₂O
                  
                  4 Li + O₂ ---> 2Li₂O
                  
               3. both group 1 and 2 metals also react with sulfur to produce sulfides
                  Rb + S₈ ---> Rb₂S
                  
                  16Rb + S₈ ---> 8Rb₂S
                  
                  Ba + S₈ ---> BaS
                  
                  8Ba + S₈ ---> 8BaS
                  
               4. e.g. iron + oxygen ---> either iron (II) oxide or iron (III) oxide depending on the conditions under which the reaction occurs
                  2Fe + O₂ ---> 2FeO
                  4Fe + 3O₂ ---> 2Fe₂O₃
                  
               5. nonmetals also react with oxygen to form oxides
                  S₈ + 8O₂ ---> 8SO₂
                  
                  C + O₂ ---> CO₂ or
                  2C + O₂ ---> 2CO
                  2H₂ + O₂ ---> 2H₂O
                  
               6. figure 8-7 page 257
                  
               7. figure 8-8 page 257
                  
            2. Reactions of Metals with Halogens
               
               1. Group 1 and Group 2 metals react with halogens to form ionic compounds of the general form MX or MX₂
                  e.g. 2Na + Cl₂ ---> 2NaCl
                  e.g. Mg + F₂ ---> MgF₂
                  
            3. Synthesis Reactions with Oxides
               
               1. oxides of active metals react with water to form hydroxides
                  e.g. CaO + H₂O ---> Ca(OH)₂
                  calcium oxide is lime, calcium hydroxide is slaked lime, necessary in the setting of cement.
                  
               2. figure 8-9 page 258
                  
               3. oxides of elements in the upper right of the periodic table form oxyacids
                  e.g. SO₂ + H₂O ---> H₂SO₃
                  2H₂SO₃ + O₂ ---> 2H₂SO_{4
                  oxygen from air to produce sulfuric acid which produces acid rain}
                  
               4. some metal oxides react with nonmetal oxides to form salts
                  e.g. CaO + SO₂ ---> CaSO₃
                  
                  Homework: Chapter 8, 8.4
                  
                  
      3. Decomposition Reactions
         decomposition reaction - definition
         
         1. AX ---> A + X where AX is a compound and A and X can be elements or compounds
            
         2. usually need some form of energy for the reaction to take place e.g. heat or electricity
            
         3. reverse of synthesis reactions
            
         4. Decomposition of Binary Compounds
            
            1. simplest type
               
            2. 2H₂O -----> 2H₂ + O₂ with the help of electricity -- direct current
               
            3. electrolysis - definition
               
            4. oxides of metals located in the lower center of the periodic table decompose into elements when heated
               e.g. 2HgO + heat ---> 2Hg + O₂
               
         5. Decomposition of Metal Carbonates
            
            1. metal carbonate + heat ---> metal oxide and carbon dioxide gas
               e.g. CaCO₃ + heat ---> CaO + CO₂
               
         6. Decomposition of Metal Hydroxides
            
            1. metal hydroxide + heat ---> metal oxide + water
               e.g. Ca(OH)₂ + heat ---> CaO + H₂O
               exception is group 1 metal hydroxides
               
         7. Decomposition of Metal Chlorates
            
            1. metal chlorate + heat ---> metal chloride + oxygen
               e.g. 2KClO₃ + heat ---> 2KCl + 3O_2, uses MnO₂ as a catalyst
               
         8. Decomposition of Acids
            
            1. some acid ---> nonmetal oxides and water
               e.g. H₂CO₃ ---> CO₂ + H₂O
               
               Homework: Chapter 8, 8.5
               
               
      4. Single Replacement Reaction
         also known as a displacement reaction
         single replacement reaction - definition
         A + BX ---> AX + B or
         Y + BX ---> BY + X where A, B, X and Y are elements and AX and BY are compounds
         
         1. Replacement of a Metal in a Compound by Another Metal
            e.g. 2Al + 3Pb(NO₃)₂ ---> 3Pb + 2Al(NO₃)₃
            
         2. Replacement of Hydrogen in water by a Metal
            
            1. for most active metals e.g. group 1 the products are hydroxide and hydrogen gas
               e.g. 2Na + 2H₂O ---> 2NaOH + H₂
               
            2. for less active metals the products are an oxide and hydrogen gas
               e.g. 3Fe + 4H₂O ---> Fe₃O₄ + 4H₂
               
         3. Replacement of Hydrogen in an Acid by a Metal
            1. more active metals react with certain acid solutions -- hydrochloric acid and sulfuric acid
            2. products are usually hydrogen gas and a salt
            3. salt is the metal + the anion of the acid
         4. Replacement of Halogens
            1. one halogen replaces another
            2. can only replace a halogen below it not above it
            3. e.g. chlorine can replace bromine but not fluorine
               
               Homework: Chapter 8, 8.6
               
               
      5. Double Replacement Reactions
         double replacement reaction - definition
         
         one of the compouds formed may be a) a precipitate b) an insoluble gas that bubbles out of the solution; c) a molecular compound that bring the ions together
         
         general equation is
         AX + BY ---> AY + BX where AX and BY are solutions of ionic compounds
         
         1. Formation of a Precipitate
            occurs when the cation of one reactant combines with the anion of another reactant to form an insoluble or slightly soluble compound
            e.g.
            2KI_(aq) + Pb(NO₃)_2(aq) ---> PbI_2(s) + 2KNO_3(aq)
            
            the potassium and nitrate ions remain in solution just as they were as reactants -- they are not active participants in this reaction -- spectator ions
         2. Formation of a Gas
            1. one product is an insoluble gas which bubbles out of the solution
            2. e.g. FeS_(s) + 2HCl_(aq) ---> H₂S_(g) + FeCl_2(aq)
         3. Formation of Water
            1. water is a stable molecular compound formed when H⁺ and OH^- ions come together
            2. e.g.
               HCl_(aq) + NaOH_(aq) ---> NaCl_(aq) + H₂O<sub>(l)
               
               Homework: Chapter 8, 8.7</sub>
               
      6. Combustion Reactions
         1. combustion reaction - definition
         2. figure 8-13
            reaction is 2H_2(g) + O_2(g) ----> 2H₂O_(g)
         3. e.g.
            C₃H_8(g) + 5O_2(g) ---> 3CO_2(g) + 4H₂O<sub>(g)
            
            Homework: Chapter 8, 8.8</sub>
            
   7. Activity Series of the Elements
      1. activity series - definition
      2. order determined by single replacement reactions
      3. most active elements on top
      4. an element can replace all elements below it but not above it
      5. table 8-3 page 266
      6. used to predict if a chemical reaction will occur
      7. 2Al_(s) + 3ZnCl_2(aq) ---> 3Zn_(s) + 2AlCl_3(aq)
      8. Co(s) + 2NaCl(aq) ---> no reaction
      9. order of activity series is based on experiments
      10. notice reaction with acids and with water, both cold and hot
          
          Homework: Chapter 8, 8.9
          
          

end of notes

A chemical reaction is the process by which one or more substances are changed into one or more different substances. back

Reactants are the original substances on the left of the chemical reaction. Back

Products are the resulting substances on the right of the chemical reaction. Back

The Law of Conservation of Mass states the total mass of the reactants must equal the total mass of the products for any given chemical reaction. Back

A chemical equation represents, with symbols and formulas, the identities and relative amounts of the reactants and products in a chemical reaction. Back

A precipitate is a solid that is produced as a result of a chemical reaction in solution and that separates from the solution. Back

A coefficient is a small whole number that appears in front of a formula in a chemical equation. Back

A word equation is an equation in which the reactants and products in a chemical reaction are represented by words. Back

A formula equation represents the reactants and products of a chemical reaction by their symbols or formulas. Back

A catalyst is a substance that changes the rate of a chemical reaction but can be recovered unchanged. Back

A reversible reaction is a chemical reaction in which the products reform the original reactants. Back

A synthesis reaction (composition reaction) is a chemical reaction in which two or more substances combine to form a new compound. Back

A decomposition reaction is a chemical reaction in which a single compound undergoes a reaction that produces two or more simpler substances. Back

Electrolysis is the decomposition of a substance by a direct current. (DC) back

A single replacement (displacement reaction) reaction is a chemical reaction in which one element replaces a similar element in a compound. Back

A double replacement reaction is a chemical reaction in which the ions of two compounds exchange places in an aqueous solution to form two new compounds. Back

A combustion reaction is a chemical reaction in which a substance combines with oxygen, releasing a large amount of energy in the form of light and heat. Back

The activity series is a list of elements organized according to the ease with which the elements undergo certain chemical reactions. Back