Chemical Reactions

							 Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
     Signs of Chemical Change

Change in        Color Change
temperature
(energy)



Formation of      Formation of
precipitate       gas
 Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
        Conservation of Mass
► Antoine   Lavoissier - Father of Chemistry

                • developed rules of
                  quantitative chemistry
                • measured the masses of all
                  reactants and products
                • Law of Conservation of Mass
Law of Conservation of Mass




► What   goes in….must come out!
         Balancing Equations
► Reactants  = substances combined that go
  into the reaction
► Products = new substances formed that
  come out of the reaction
      Reactants  Products
          Balancing Equations
► law of conservation of mass: mass of the
  reactants must equal mass of the products
  mass Reactants  mass Products



► We  now know that (#atoms)(atomic mass) = mass
► This means that:

 #atoms Reactants  #atoms Products
     Rules - Balancing Equations
1. Count the atoms of one element on both
   sides of the equation
     N2 + H2  NH3
2. Use coefficients (multiples) to increase
   atoms of an element
     N2 + 3H2  2NH3
3. NEVER change a formula (change/insert a
   subscript)
     N2 + H3  N2H3
Balancing Reactions
 Al + O2    Al2O3
     Balancing Equations - practice
1.     H2 +   O2 ---->    H2O



2.     Mg +   P4 --->    Mg3P2


3.     Cu +   O2 ---->    Cu2O
     Balancing Equations - tips
► Lookfor polyatomic ions
► Count the ion as a unit


 CaCl2 + AgNO3 ----> AgCl + Ca(NO3)2
    Balancing Equations - tips
► Checkfor elements that occur more than
 once on one side of an equation – sum the
 atoms.

 (NH4)2CO3 ---> NH3 + CO2 + H2O
        Balancing Equations - tips
►    If you are balancing a combustion
     reaction, balance in this order:
            1.   Balance C
            2.   Balance H
            3.   Check if the coefficient in front of H2O is odd or even
            4.   Double coefficients (except O2) if odd
            5.   Balance O2


            C2H6 + O2  CO2 + H2O

    http://dbhs.wvusd.k12.ca.us/webdocs/Equations/Balance-Equation.html
 Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
             Organic Compounds
► Organic   compound = a compound containing
  carbon atoms
► Derived from living tissues
► ALL organic compounds must contain
  carbon, but not all compounds that contain
  carbon are organic!
           Organic Compounds
► Carbon  atoms have     valence electrons.
►  carbon atoms must bond        times.
► The element that most commonly bonds to
  carbon is hydrogen
                   Methane
► Methane  (CH4) : the simplest organic molecule
► Used for chemistry lab burners
            Hydrocarbons
► Hydrocarbon = a molecule formed by a
 chain of carbon atoms with hydrogen atoms
 bonding to the chain
                      Alkanes
► Alkane  = generic name for all
  hydrocarbons that have only single bonds
  between atoms in the carbon chain
► The prefix “alk-” is changed to show how
  many carbon atoms are in the chain
           1 – meth       6 – hex
           2 – eth        7 – hept
           3 – prop       8 – oct
           4 – but        9 – non
           5 – pent       10 - dec
                Alkanes
 Name       Structural   Ball and Stick
Molecular    Formula       Model
 Formula
        Alkenes and Alkynes
► Alkene = has a
 double bond in the
 carbon chain



► Alkyne  = has a
 triple bond in the
 carbon chain
           Determining Formulas
►   There are 2 methods for determining a
    formula from a name:
    1. Draw the molecule and count the carbons and
       hydrogens
       Draw propene:
    2. Use the following formulas:
      a)   Alkane: #H = 2(#C) + 2
      b)   Alkene: #H = 2(#C)
      c)   Alkyne: #H = 2(#C) - 2
  Organic Nomenclature
Name     Molecular   Structural
         Formula      Formula




           C5H8


butane
                Aromatics
► Aromatic:    is a “cyclic” hydrocarbon
► Cyclic hydrocarbons form ring structures
  instead of chains
► Cycloalkanes have distinct odors
               Aromatics
► Benzene:  an important cyclic hydrocarbon
 used in industrial applications
Aromatics
 Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
              Writing Equations
►    Equation: shorthand for writing a
     chemical reaction (more formulas!)
►    Remember the 7 diatomic elements:
     H,N,O,F,Br,Cl,I
►    Symbols:
    1. Yields, forms, makes: ()
    2. Solid (s) or precipitate (), liquid (l), gas (g)
       or (), aqueous (aq)
            Writing Equations
1.   Hydrogen and oxygen combine to yield
     water.



2.   Calcium carbonate and hydrochloric acid
     react to form water, carbon dioxide, and
     calcium chloride.
 Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
               Synthesis
► Synthesis  (combination): forming 1
  substance from 2 or more substances
► General form:
           A + B  AB
► Specific Example:
           H2 + O2  H2O
*Key: look for one product
            Decomposition
► Decomposition:  the breaking down of 1
  substance into 2 or more substances
► General Form:
           AB  A + B
► Specific Example:
           CaCO3  CaO + CO2
*Key: Look for 1 reactant
      Displacement Reactions
► Displacement   : one thing takes the place
 of or pushes out another thing


                              Water displaced
                              by a rock
            Single Displacement
► General   Form:
    Ann-Tom + Crystal  Crystal-Tom + Ann
            AT + C  A + CT
► Specific Example:
            Zn + HCl  ZnCl2 + H2

   Single displacement: the replacement of 1 element
    in a compound by another

*Key: Look for 1 element plus 1 compound on both
  sides of the reaction
          Single Displacement



► AgNO3   + Cu  ???
             Double Displacement
► General    Form:
    Ann-Bob + Crystal -Tom Crystal-Bob + Ann-Tom
              AB + CT  CB + AT

► Specific   Example:
              Na2O + FeCl3  Fe2O3 + NaCl

   Double displacement: the replacement of 1
    element in a compound by another element from
    a 2nd compound

*Key: Look for 2 compounds on both sides of the reaction
         Double Replacement
1.   HCl + NaHCO3 




1.   PbNO3 + KI 
Activity Series
               Activity Series
►   Activity series : a list in order of reactivity
    of elements
►   Practice: determine if the following single
    replacement reactions will occur
    1) Pb + MgCO3 
    2) Li + CuCl2 
    3) Na + H2O 
                 Solubility
► Solubility = the ability of an ionic
  compound to dissociate to its ions in water
► Ex: NaCl(s)  Na+(aq) + Cl-(aq)
                  Solubility
► Some   salts are soluble (above), some aren’t.




    Strong bonds between the ions may
    prevent them from dissociating.
Solubility Rules
Solubility Rules
        Precipitation Reaction
►A  precipitate is a solid that forms out of
  solution.
► A precipitation reaction is a double
  displacement reaction that occurs
► NO reaction occurs if a precipitate does NOT
  form
       Precipitation Reaction
                ► Soluble NaCl + soluble
                  AgNO3 are reacted.
                ► AgCl and NaNO3 are the
                  possible products after
                  displacement
                ► the solubility rules are
                  used to determine that
                  AgCl is NOT soluble.
AgNO3(aq) + NaCl(aq)  NaNO3(aq) + AgCl(s)
         Precipitation Reactions
►   Will the following double displacement
    reactions occur?
►   If so, what is the formula for the
    precipitate?

    1) PbNO3 + NaCl 

    2) Li2SO4 + NH4Br 
          Predicting Products
► In order to predict the products of a
  reaction, first classify the reaction.
► Use the Activity Series or the Solubility
  Rules where applicable.
 Chemical Reactions
1.   Signs of Chemical Change
2.   Conservation of Mass
3.   Organic Compounds
4.   Writing Equations
5.   Classifying Reactions
            Review Reactions
1.   Signs of Chemical Change
2.   Writing Equations
3.   Balancing Equations
4.   Classifying Reactions
5.   Predicting Products
6.   Stoichiometry
     Signs of Chemical Change
1.

2.

3.

4.
               Writing Equations
1.   Writing   Molecular Formulas
2.   Writing   Ionic Formulas
3.   Writing   Organic Formulas
4.   Writing   Acid Formulas
         Balancing Equations
► Use coefficients only
► Add all atoms of same element on one side
► Use subscripts for element AFTER it
► Use subscripts for all polyatomic ions in
  parentheses
► Solve odd-even problems by doubling all
  coefficients
        Balancing Equations
1.   N2 + H2      NH3

2.   C2H6 + O2     CO2 +   H2O

3.   P4 + O2      P2O5
         Classifying Reactions
1.   Synthesis: 1 product
2.   Decomposition: 1 reactant
3.   Single Replacement: element +
     compound
4.   Double Replacement: compound +
     compound
5.   Combustion: hydrocarbon + O2  CO2 +
     H2O
             Predicting Products
► Classify   reaction and finish based on type of
  reaction
► Use the reference package for help!!
► Use Activity Series for SR reactions
► Use Solubility Rules for DR reactions
             Stoichiometry
► Mol-mol  problems: 1 step
     - this is the ONLY step that can be used
     to switch from one substance to another!
► Mol-mass problems: 2 steps
► Mass-mass problems: 3 steps
► 2 givens: 2 problems
     - limiting reagent: reactant that makes
       less product
     - % yield = actual/theoretical
                 = lab/calculated