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					                                                           CHEMICAL REACTIONS

Table of Contents                                                      Evidence of a Chemical Reaction
     1. Physical and Chemical Changes                                  Solid Formation (precipitation)
     2. Understanding Chemical Changes                                  3NaOH + AlCl3  Al(OH)3 + 3NaCl
     3. Chemical Equations                                                                 white ppt
     4. Balancing Chemical Equations                                   2. Color Change
     5. Types of Chemical Reactions                                    Pb(NO3)2 + 2KI  PbI2 + 2KNO3
1. Physical and Chemical Changes                                                         yellow ppt
Warm up                                                                3. Gas Release
     • List down some changes around you and identify them               CaCO3 + 2HCl  CaCl2 + CO2 + H2O
          as physical and chemical.                                    4. Heat Exchange
     • Which changes in your list are reversible and which are           2Al + Fe2O3  2Fe + Al2O3 + Energy
          irreversible?
     • Which changes in your list produce new substances?              Section Review
Physical changes are changes in which the identity of a                    1. What are the indicators for the chemical reaction of
substance does not change. Chemical composition of substances                   combustion of gasoline in engines?
remain unchanged. Breaking of a glass, cutting of a sheet of               1. Gas formation, heat exchange, color change
paper, dissolving of salt in water, freezing of water…etc are
physical changes.                                                          2.  Which observation does NOT indicate that a chemical
         • No new substance is formed.                                         reaction has occurred?
         • Some physical changes are reversible.                               A. formation of a precipitate
Changes that cause to produce new substances are called                        B. production of a gas
chemical changes. The rusting of iron, boiling of an egg, spoiling             C. evolution of energy
fruits, burning of coal…etc. are chemical changes. Chemical                    D. change in total mass of substances
changes usually irreversible.                                               3. A solid produced by a chemical reaction that then
Section Review                                                                 separates from the solution is called a(n) _________
     1. Identify the following changes as physical or chemical.             4. A solid produced by a chemical reaction that then
          Burning of wood, evaporation of alcohol, freezing of                 separates from the solution is called a(n) precipitate.
          cement, frying of egg, souring of milk, digging of soil,     3. Chemical Equations
          painting of a wall, cleaning of dishes.                      Warm up
     1. Chemical changes: Burning of wood, frying of egg,                   • Write some word equations that represent the
          souring of milk, cleaning of dishes.                                 chemical changes given below.
                                                                       Baking a cake, souring milk, burning a piece of paper, rusting
    2.   Physical changes: Evaporation of alcohol, digging of          iron
         soil, painting of a wall. Which of the following changes           • A chemical equation shows the chemical formulas and
         is different?                                                         relative amounts of all reactants and products.
           A. Raining                                                       • A substance that undergoes a reaction is called a
           B. Sublimation of iodine                                            reactant.
           C. Combustion of gasoline                                        • When reactants undergo a chemical change, each new
           D. Distillation of petroleum                                        substance formed is called a product.
                                                                       methane + oxygen  carbon dioxide + water
    3.   Wood that has burned and formed carbon dioxide and            CH4 + O2            CO2      + H2O
         water vapor has gone through a
          A. chemical change
          B. physical change
          C. change in state
          D. change in color.

2. Understanding Chemical Changes
Warm up
     • List some evidences that suggest that a chemical
           reaction has occurred and decide which of them might
           be indicator for the following changes.
  Cooking of cake, photosynthesis, burning of paper, spoiling of
fruits, cleaning of a cloth.
In chemical reactions following properties remain constant.         4. Balancing Chemical Equations
     • Types and number of reacting atoms,                          Warm up
     • Total mass of substances.                                        • Describe the mass change in the burning of a wood.
     • Total number of protons, neutrons, and electrons.                • Think a way that proves mass does not change in
In chemical reactions following properties may change.                       chemical reactions.
     • Number of electrons and electronic configurations of         Conservation of Mass
        atoms.                                                          • The law of conservation of mass states that mass is
     • Total number of moles, molecules and volumes.                         neither created nor destroyed during chemical
     • Physical properties like color, odor, taste and states.               reactions. Total mass is constant in a chemical reaction.
                                                                             This is known as Lavoisier’s Law.
Section Review                                                          • The number of atoms for each element must be the
    1. Knowledge about what products are produced in a                       same on the reactants’ side and on the products’ side.
         chemical reaction is obtained by                               • A coefficient multiplies the number of atoms of each
         A. inspecting the chemical equation.                                element in the formula that follows.
         B. balancing the chemical equation.                                      • H2O: 2 hydrogen atoms, 1 oxygen atom
         C. laboratory analysis.                                                  • 2H2O: 4 hydrogen atoms, 2 oxygen atoms
         D. writing a word equation.                                Below are some tips for balancing equations:
                                                                        • Take the coefficients of the most complex compound as
    2.   A chemical reaction has NOT occurred if the products                one.
         have                                                           • Balance the elements found in this most complex
         A. the same mass as the reactants.                                  compound first.
         B. less total bond energy than the reactants.                  • Balance the elements last that is free in reactants or
         C. more total bond energy than the reactants.                       products.
         D. the same chemical properties as the reactants.              • Balance oxygen and hydrogen atoms at the end.
                                                                    Never change the subscripts
    3.   Which word equation represents the reaction that           Sample Problem A
         produces water from hydrogen and oxygen?                   Balance the equation for the reaction of iron(III) oxide with
         A. Water is produced from hydrogen and oxygen.             hydrogen to form iron and water.
         B. Hydrogen plus oxygen yields water.                      Sample Problem A Solution
         C. H2 + O2  water.                                                 1 Fe2O3 + 3H2  2Fe + 3H2O
         D. Water can be separated into hydrogen and oxygen         Sample Problem B
                                                                    Balance the equation below with integer numbers.
    4.   How would oxygen be represented in the formula             Na + H2O  NaOH + H2
         equation for the reaction of methane and oxygen to         Sample Problem B Solution
         yield carbon dioxide and water?                                      1Na + 1H2O  1NaOH + 1/2H2
         A. oxygen                                                  Then,
         B. O2                                                                2Na + 2H2O  2NaOH + 1H2
         C. O                                                       Sample Problem C
         D. O3                                                      Aluminum reacts with arsenic acid, HAsO3, to form H2 and
                                                                    aluminum arsenate. Write a balanced equation for this reaction.
    5.   In an equation, the symbol for a substance in water        Sample Problem C
         solution is followed by                                             1Al + 3HAsO3  3/2H2 + 1Al(AsO3)3
         A. (l).                                                    Then,
         B. (g).                                                              2Al + 6HAsO3  3H2 + 2Al(AsO3)3
         C. (aq).                                                   Sample Problem D
         D. (s).                                                    Find the unknown substance represented by X in the following
                                                                    balanced equation.
    6.   Photosynthesis is the process plants use to make                    4FeS2 + 11O2  2Fe2O3 + 8X
         glucose and oxygen gas from carbon dioxide and water       Sample Problem D
         only in the presence of light. Write a word equation for            4FeS2 + 11O2  2Fe2O3 + 8SO2
         the reaction.
                                                                    Section Review
                                                                        1. What is the small whole number that appears in front
                                                                             of a formula in a chemical equation?
                                                                             A. a subscript
                                                                             B. a superscript
                                                                             C. a ratio
                                                                             D. a coefficient
    2.   According to the law of conservation of mass, the total        • Here are some examples;
         mass of the reacting substances is                        NH4NO3  N2O + 2H2O
         A. always more than the total mass of the products        2H2O2  2H2O + O2
         B. always less than the total mass of the products.       2NaCl  2Na + Cl2
         C. sometimes more and sometimes less than the total       PCl5  PCl3 + Cl2
              mass of the products.
         D. always equal to the total mass of the products.        3. Single Displacement Reactions
    3.   A chemical equation is balanced when the                       • In a displacement reaction a single element reacts with
         A. coefficients of the reactants equal the coefficients             a compound and displaces another element from the
              of the products.                                               compound.
         B. same number of each kind of atom appears in the             • Displacement reactions can be illustrated;
              reactants and in the products.                                  A + BC  B + AC
         C. products and reactants are the same chemicals.              • Single displacement reactions mostly take place due to
         D. subscripts of the reactants equal the subscripts of              activity differences of elements. A more active element
              the products.                                                  displaces a less active one.
    4.   When the equation Fe3O4 + Al  Al2O3 + Fe is correctly    Zn(s) + CuSO4(aq)  Cu(s) + ZnSO4(aq)
         balanced, what is the coefficient of Fe?                   Fe(s) + NaCl(aq)  No reaction
         A. 3       B. 4       C. 6  D. 9                          Activity of Some Metals
    5.   Which coefficients correctly balance the formula          Li Rb K Ba Sr Ca Na Mg Al Mn Zn Cr Cd Fe Co Ni Sn Pb
         equation                                                  H Cu Hg Ag Pt Au (Activity Decreases )
         NH4NO2(s)  N2(g) + H2O(l)?                               Activity of Some Nonmetals
         A. 1, 2, 2                                                F Cl Br I (Activity Decreases )
         B. 1, 1, 2                                                Some examples;
         C. 2, 1, 1                                                NaBr(aq) + Cl2(g)  2NaCl(aq) + Br2(g)
         D. 2, 2, 2                                                Ca(s) + 2H2O  Ca(OH)2(aq) + H2(g)
    6.   What is the formula of the compound represented by X      Mg(s) + 2CuCl(aq)  MgCl2(aq) + 2Cu(s)
         in the following balanced equation?
                    2Ag + 2H2SO4  Ag2SO4 + SO2 + 2X               4. Double Displacement (Metathesis) Reactions
         X: H2O                                                        • In a double-displacement reaction two compounds in
    7.   How many grams of water is produced from 8 g                      aqueous solution appear to exchange ions and form
         hydrogen and 64 g oxygen gases?                                   two new compounds.
         2H2 + O2  2H2O                                               • One of the products must be a solid precipitate, a gas,
         Following the conservation of mass law                            or a molecular compound, such as water.
         mreactants= mproducts                                         • Double displacement reactions can be illustrated;
         8 g + 64 = 72 g H2O will be produced                              AB + CD  AD + CB
                                                                       • Some examples;
5. Types of Chemical Reactions                                     HCl(aq) + NaOH(aq)  HOH(l) + NaCl(aq)
Warm up                                                            Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(ppt) + 2KNO3(aq)
     • Describe the following terms
Synthesis, Analysis, Decomposition, Combination, Oxidation,        5. Endothermic and Exothermic Reactions
Combustion, Neutralization, Displacement                           A reaction which absorbs energy is endothermic reaction and
     • What kind of reactions exist in human body?                 which release energy is exothermic reaction
5. Types of Chemical Reactions                                          • Some examples;
1. Combination (Synthesis) Reactions
                                                                   Ca(s) + 2H2O(l)  Ca(OH)2(aq) + H2(g) + Energy
     • Whenever two or more substances combine to form a
                                                                                                      Exothermic Reaction
         single product, the reaction is called a synthesis
                                                                   H2O(l) + Energy  H2(g) + O2(g) Endothermic Reaction
         reaction.
                                                                   6. Combustion Reactions
     • Combination reactions can be illustrated;
                                                                   A combustion reaction is a reaction of a carbon-based
                     A + B  AB
                                                                   compound with oxygen.
     • Here are some examples;
                                                                        • Some examples;
C + O2  CO2, 4Fe + 3O2  2Fe2O3
                                                                   C3H8 + 5O2  3CO2 + 4H2O + heat
CaO + H2O  Ca(OH)2 , N2 + 3H2  2NH3
                                                                   CH3CH2OH + 3O2  2CO2 + 3H2O + heat
                                                                   C6H12O6 + 6O2  6CO2 + 6H2O + heat
2. Decomposition (Analysis) Reactions
    • In a decomposition reaction a single compound breaks
        down, often with the input of energy, into two or more
        elements or simpler compounds.
    • Decomposition reactions can be illustrated;
                      AB  A + B
Section Review
1. In what kind of reaction do two or more substances combine
to form a new compound?
     A. decomposition reaction
     B. double-displacement reaction
     C. ionic reaction
     D. synthesis reaction
2. In what kind of reaction does a single compound produce two
or more simpler substances?
     A. decomposition reaction
     B. displacement reaction
     C. synthesis reaction
     D. ionic reaction
3. The reaction 2KClO3(s)  2KCl(s) + 3O2(g) is a(n)
     A. synthesis reaction.
     B. combustion reaction.
     C. decomposition reaction.
     D. ionic reaction.
4. In what kind of reaction does one element replace a similar
element in a compound?
     A. displacement reaction
     B. decomposition reaction
     C. combustion
     D. ionic reaction
5. The reaction Cl2(g) + 2KBr(aq)  2KCl(aq) + Br2(l) is a(n)
     A. synthesis reaction.
     B. displacement reaction.
     C. ionic reaction.
     D. combustion reaction.
6. A precipitate forms in a double-displacement reaction when
     A. hydrogen gas reacts with a metal.
     B. positive ions combine with negative ions.
     C. water boils out of the solution.
     D. a gas escapes.
7. I. K2CO3 + Cr  , II. ZnI2 + Br2  , III. CuSO4 + Zn 
Which of the above reaction(s) take place under appropriate
conditions?
     A. A. I only      B. II only    C. II and III      D. I and llI
8. Which of the following is a combustion reaction?
     A. A. N2 + 3H2  2NH3
     B. B. H2O  H2 + 1/2O2
     C. C. CaCO3 + heat  CaO + CO2
     D. D. C3H8 + 5O2  3CO2 + 4H2O

				
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