Chemistry chapter 8 sections 8-1 & 8-2 pages 240 – 264.

 

Balancing Equations, Types of Reactions, and Predicting Products

I.  Chemical equations

      Chemical equations represent the net effect of a chemical reaction. 

            (reactants react to produce products)

      A.  Reactants:  the starting materials in a      chemical reaction,  written on the left side of the arrow

      B.  Arrow:  like an equal sign

      C.  Products:  the ending materials in a chemical reaction,  written on the right side of the arrow

      D.  Symbols found in equations:  found like a subscript after a compound formula

            1.  (cr) or (s):  crystal, in the solid state

            2.  (l):  liquid

            3.  (g):  gas

            4.  (aq):  aqueous, substance is dissolved in water and is in the form of a solution

      E.  Law of Conservation of Mass:  mass is neither created nor destroyed – the total starting mass of the reactants must equal the total ending mass of the products 

II.  Balancing Equations

      A.  Correct formulas

            1.  compounds have a net charge of zero

            2.  know the seven diatomic molecules

            3.  know the acid formulas and names

      B.  the total number of atoms of each element in the reactants must be equal to the total number of atoms of that element in the products

      C.  if atoms are not balanced - balance them with a coefficient placed in front of the entire compound that contains that element (this means every element in that compound is multiplied by that coefficient)

      D.  elements and compounds react moles-to-moles, so the coefficients represent the number of moles of the element or compound that is needed to react with another substance

III.  Types of reactions

      A.  Exchange Reactions:  Double Displacement (DD) (also called metathesis) - two elements or ions switch places

                        comp AB  +  comp CD  Õ  comp AD  +  comp CB

            1.  Precipitation reaction - formation of a solid

            2.  Acid-Base reaction - formation of water

            3.  Gas producing reactions - formation of an insoluble gas

      B.  Oxidation-Reduction Reactions:  exchange of electrons between compounds and/or elements    

            1.  Combustion (C) (when something burns in oxygen): 

                  a.  organic hydrocarbon compounds:  combine with oxygen forming carbon dioxide and water

                        comp CxHy  +  O2  Õ  CO2  +  H2O

                  b.  inorganic compounds:  compound “splits” and each combines with oxygen forming oxides

                        compound AB  +  O2  Õ  AO  +  BO

                  c.  elements  or compounds can combine with oxygen also

                        element A  +  O2  Õ  AO

                        compound AB  +  O2  Õ  ABO

            2.  Single Displacement (SD):  one element takes the place of another element in a compound

                  a.  if element A forms positive ions, then it takes the place of B in the compound

                        ele A  +  comp BC  Õ  comp AC  +  ele B

                  b.  if element A forms negative ions, then is takes the place of C in the compound 

                        ele A  +  comp BC  Õ  comp BA  +  ele C

            3.  Synthesis (S):  "putting together" of elements or compounds with other elements or compounds

                  ele A  +  ele B  Õ  comp AB  or comp BA

                  ele A  + comp BC  Õ  comp ABC  (or variation)

                  comp AB  +  comp CD  Õ  comp ABCD

 

            4.  Decomposition (D):  "taking apart" a compound to form two or more elements or compounds

                  a.  oxy-acids:  (acids with oxygen in them such as:  H2SO4   HNO3   H2CO3   H3PO4   etc.

                        Õ  nonmetal oxide  + water

                  b.  metallic hydroxide  ( - OH )

                        Õ  metal oxide  + water

                        (metals are element on the left side of the chart)

                  c.  metallic carbonate  ( - CO3 )

                        Õ  metal oxide  + carbon dioxide

                  d.  metallic hydrogen carbonate  ( - HCO3 )

                        Õ  metal oxide  + carbon dioxide  +  water

                  e.  metallic chlorate family  ( - ClO,  or  - ClO2,  or  - ClO3,  or  - ClO4)

                        Õ  metal chloride  +  oxygen

                  f.  metallic oxide  ( - O )

                        Õ  metal  +  oxygen

                  g.  compound breaking into the elements that make it up

IV.  Predicting Products

A.  Determine what type of reaction the reactants suggest

B.  Predict what “goes together” on the product side

C.  Write the correct formulas for the products

D.  Balance the equation