Types of Chemical Reactions: Synthesis

 

Synthesis (composition):
 

  • two or more representative particles (elements or compounds) may combine to form a more complex compound.

  • The number of particles decreases from reactants to products

    •

  • Basic form: A  +  X  -->    AX

1. Examples of synthesis reactions:

 

       a. Two elements form a compound 

- Metal  +  oxygen  -->   metal oxide

    Ex. 2Mg(s)  +  O2(g)  -->    2MgO(s)

 

-Nonmetal  +  oxygen  -->    nonmetallic oxide

    Ex. C(s)  +  O2(g)  -->    CO2(g)

 

- Metal + nonmetal  -->    salt

  Ex. 2 Na(s)  +  Cl2(g)  -->    2NaCl(s)

 

- A few nonmetals combine with each other.

   Ex. 2P(s)  +  3Cl2(g)  -->    2PCl3(g)

     

     b. Metal chlorides react with oxygen gas to product metal chlorates

           Ex. CaCl2(s)  +  3 O2(g)  -->  Ca(ClO3)2(s)

 

       c. Metal oxides react with carbon dioxide to produce metal carbonates

             Ex.  Na2O(s)   +  CO2(g)  -->  Na2CO3(s)

     

     d. Metal oxide  +  water  -->    metallic hydroxide

Ex. MgO(s)  +   H2O(l)  -->    Mg(OH)2(s)

 

-soluble metal hydroxides are bases in solution. So metal oxides are considered basic anhydrides

      e. Nonmetal oxide  +  water  -->    ternary acid

            General equation: EOx + yH2O → H2yEOx+y

 

Ex. CO2(g)  +  H2O(l)  -->  H2CO3(aq)

 

-nonmetal oxides are sometimes referred to as acidic anhydrides.

-Note: the oxidation state of the nonmetal in the oxide and acid is unchanged.

 

2. These two reactions must be remembered:

 

         a. N2(g)  +  3H2(g)  -->    2NH3(g)

           -this is known as the Born-Haber process

 

         b. NH3(g)  +  H2O(l)  -->    NH4OH(aq)

 

3. Most synthesis reactions are driven by Redox mechanisms

  • Redox is short for reduction-oxidation reactions. These two coupled reactions are associated with the change in elemental oxidation states by the movement of electrons.

  • Electron movement can be seen as transferring electrons (ionic bond formation) or redistribution of electrons in orbitals (covalent bond formation).

  • Reduction is the gaining of electrons (think reduce charge by gaining electrons). Elements with higher pulls typically are reduced

  • Oxidation is the losing of electrons. Elements with lower pulls typically are oxidized.