CHEMICAL REACTIONS AND EQUATIONS

 

1.         IN A CHEMICAL REACTION, SUBSTANCES CALLED THE REACTIONS ARE CONVERTED INTO SUBSTANCES CALLED PRODUCTS.

2.         CHEMICALS REACT TO BECOME MORE STABLE.

3.         CHEMICAL REACTIONS ARE REPRESENTED BY CHEMICAL EQUATIONS THAT ARE SHORTHAND SENTENCES.  THEY ARE MADE UP OF THE FOLLOWING:

            A.        SYMBOLS = ELEMENTS EX. CO COBALT

                        SYMBOLS REPRESENT ATOMS

            B.         FORMULAS = 2 OR MORE ATOMS COMBINED EX. O2

                        THIS IS NO LONGER AND ATOM IT IS 2 ATOMS

                        COMBINED FORMING A MOLECULE

ANOTHER EX. CO THIS IS A MOLECULE OF CARBON                               MONOXIDE.

                        TWO ATOMS COMBINED MAKES A MOLECULE

            C.        2 Co = 2 ATOMS OF COBALT.  THE 2 IS THE COEFFICIENT

                        AND TELLS HOW MANY ATOMS OR MOLECULES ARE THERE.

            D.        02 = 1 MOLECULE OF OXYGEN.  THE 2 IS A SUBSCRIPT AND           

                        TELLS HOW MANY ATOMS OR MOLECULES ARE THERE.

            E.         + = REACTS WITH ON REACTANTS SIDE OR AND ON PRODUCTS

                        SIDE

            F.         → OR = MEANS TO FORM

 

REACTANTS     PRODUCTS

 

                                    EX.       2 Ca + 02               → 2Ca0

                                                 COEFFICIENT             SUBSCRIPT

 

2 ATOMS OF CALCIUM REACTS WITH 1 MOLECULE OF OXYGEN

TO FORM 2 MOLECULES OF CALCIUM OXIDE

           

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

TYPES OF CHEMICAL REACTIONS

 

1.         THERE ARE MANY TYPES OF CHEMICAL REACTIONS.

            HOWEVER MOST REACTIONS FALL INTO 4 BASIC TYPES.

 

            A.        DIRECT COMBINATION                 A    +    B    →     AB

 

                                                2  Na  +  C12   →   2  NaCl

 

            B.         DECOMPOSITION                AB                               A     +    B

 

                                                2 H2O     →   2 H   +    O

 

            C.        SINGLE REPLACEMENT                 A     +    BX   →    AX   +   B

 

                                                Zn   +   2HCl      →    ZnCl2    +    H2

 

                D.        DOUBLE REPLACEMENT        AX    +    BY      →      BX    +   AY

 

                                                CaCO3   +   2   HCL                      H2CO3   +  CACl2

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

BALANCING EQUATIONS

 

1.         WHEN CHEMICALS REACT THERE HAS TO BE AS MANY

            ATOMS OF AN ELEMENT ON THE REACTANT AND PRODUCT

            SIDE OF AN EQUATION.  (CONSERVATION OF MATTER)

 

2.         TO BALANCE AN EQUATION YOU CAN’T CHANGE THE

            NUMBERS WITHIN A MOLECULE.  (H2O).  THE 2 CAN’T

            CHANGE.  ELECTRONS HAVE REACHED THE OCTET RULE.

            THIS IS STABLE AND WON’T CHANGE.  YOU CHANGE THE

            NUMBERS IN FRONT OF THE MOLECULE CALLED THE

            COEFFICIENT.  THIS CHANGES THE NUMBER OF

            MOLECULES BUT NOT THE STABLE MOLECULE ITSELF.

 

3.         THE PROBLEM MOST STUDENTS HAVE IS

            UNDERSTANDING WHAT THE SYMBOLS MEAN.

            A.        2A12 (SO4) 3 MEANS THERE ARE 2

            MOLECULES WITH 2 Al IN EACH MAKING A TOTAL OF 4

            Al.  IT MEANS THERE ARE 3 SO4 POLYATOMIC IONS.

            THIS MAKES 6  S  AND 24  O  IN THE TWO MOLECULES.

 

4.         WHEN BALANCING START WITH THE SIMPLEST        

            COMBINATION FIRST.

                                    CH4  +  O2  →  CO2  +  H2O

            DON’T START WITH THE OXYGEN.  IT HAS THREE

            PLACES TO BALANCE AT ONCE.

 

5.         WHEN THE NUMBERS GET COMPLEX, USE FRACTIONS

            AND THE MULTIPLY BY A SMALL WHOLE NUMBER TO

            ELIMINATE THE FRACTION.

 

                                    Al   + O2      →    Al2O3

 

                                    2 Al    +  1 ½  O2     →     Al203

                        MULTIPLY BY 2

 

                                    4   Al      +    3   O2      →    2Al203

 

 

 

 

 

 

 

 

DETERMINGING IF SINGLE REPLACEMENT REACTIONS WILL OCCUR

 

 

  1. FOR A SINGLE REPLACE MENT REACTION TO ACTUALLY TAKE PLACE THE  SINGLE METAL OR NONMETAL HAS TO BE MORE ACTIVE THAN THE ELEMENT IT IS REPLACING IN THE COMPOUND.  TO DETERMINE  THIS, YOU MUST LOOK AT AN ACTIVITY CHART WHICH HAS THE MOST ACTIVE METALS AND NONMETALS AT THE TOP OF THE CHART.  AS YOU GO DOWN THE CHART THE ACTIVITIES GET LESS.  THE MORE ACTIVE METALS OR NONMETALS WILL REPLACE THOSE BELOW THEM.

 

DETERMINING IF A DOUBLE REPLACEMENT REACTION WILL OCCUR

 

  1. FOR A DOUBLE REPLACEMENT REACTION TO ACTUALLY OCCUR, ONE OF THE PRODUCTS HAS TO BE REMOVED AS AN AQUEOUS SOLUTION.  IF THIS DOES NOT HAPPEN THE REACTANTS REMAIN AS IONS AND IN AQUEOUS SOLUTION AND NO REACTION OCCURES.  IN THE PRODUCTS A COMPOUND CAN BE CHANGED FROM AQUEOUS IONS IN ONE OF THREE WAYS.
    1. ONE OF THE PRODUCT COMPOUNDS IS NOT SOLUABLE

AND PRECIPATATES OUT OF SOLUTION

    1. WATER IS FORMED, WHICH MAKES A MOLECULE THAT IS NOT IONS IN AQUEOUS FORM.
    2. A GAS IS FORMED BECAUSE GASES WILL NOT REMAIN AS AQUEOUS IONS.
  1. TO DETERMINE IF A DOUBLE REPLACEMENT REACTION WILL OCCUR.YOU MUST LOOK AT THE PRODUCTS TO SEE IF WATER OR A GAS FORMS.  YOU MUST ALSO LOOK AT A SOLUBILITY CHART TO SEE IF AN INSOLUABLE PRECIPITATE IS FORMED.

EX.  FeS    +  HCl     =    FeCl2  +  H2S(g)

THIS REACTS BECAUSE THE GAS IS NOT REMAINING AS IONS

Ca(NO3)2    +   2 HCl   =     2 HNO3  +  CaCl2

THIS DOES NOT REACT BECAUSE AFTER LOOKING ON THE SOLUBILITY CHART BOTH PRODUCTS ARE SOLUABLE AND REMAIN AS IONS.

Cu(OH)2   +    2 HC2H3O2     =        2 H2O    +       Cu(C2H3O2)2

             YES THIS REACTS BECAUSE WATER WAS FORMED NO LONGER REMAINGING AS IONS.

 

 

 

 

 

 

 

 

NET IONIC EQUATIONS

 

IN DOUBLE REPLACEMENT REACTIONS WHERE A PRECIPITATE OCCURS WE WOULD WRITE THE EQUATION AS FOLLOWS:

 

2NaOH (aq)    +   CuCl2(aq)          =         2 NaCl(aq)  +   Cu(OH)2(s)

 

THIS SHOWS THAT THE REACTION OCCURS BUT IT DOES NOT FULLY EXPLAIN WHAT HAPPENED.  TO SHOW THIS WE WRITE IT IN AN IONIC EQUATION FORM WHERE ALL AQUEOUS COMPOUNDS SHOW UP AS IONS IN SOLUTION BECAUSE THAT IS WHAT THEY REALLY ARE.

IONIC EQUATION:

 

2  Na+1(aq)    +   2 OH-1(aq)       +   Cu+2 (aq)    +   2Cl-1(aq) 

  =       2 Na+1 (aq)  +  2 Cl-1(aq)   +  Cu(OH)2(s)        

 

NOTICE IN THIS REACTION Na    AND Cl REMAINED IONS ON BOTH THE REACTANTS AND PRODUCTS SIDE.  SO, NOTHING CHEMICALLY HAPPENED TO THEM.  THEY ARE CALLED SPECTATOR IONS BECAUSE OF THAT.  TO MAKE A NET IONIC EQUATION YOU  CROSS OUT THE SPECTATOR IONS ON BOTH SIDES OF THE EQUATION.              

                                                                                                   

2  Na+1(aq)    +   2 OH-1(aq)       +   Cu+2 (aq)    +   2Cl-1(aq) 

  =       2 Na+1 (aq)  +  2 Cl-1(aq)   +  Cu(OH)2(s)        

THIS ELIMINATES THE 2 Na+2 IONS ON BOTH SIDES AND THE Cl-1 IONS ON BOTH SIDES LEAVING THE FOLLOWING NET IONIC EQUATION:

 

             2OH-1 (aq)   =  Cu+2(aq)   =     Cu(OH)2(s)