Chemical Reaction (Types of Chemical Reactions).ppt

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1. Chemical Reactions

2. Starter
Lets revise on writing a word equation
Potassium hydroxide and sulfuric acid as
reacted. To form potassium sulfate and
water
write the word equation for the reaction

3. Translating Word Equations to
Symbol Equations
•A skeleton equation uses chemical formulas
rather than words to identify the reactants and
products of a chemical reaction.
•The word equation
Iron (s) + chlorine (g)  iron (III) chloride (s)
•The skeleton equation
Fe(s) + Cl
2
(g)  FeCl
3
(s)
A skeleton equation is not yet “balanced” by coefficients!

4. One more example…
•6 Na (s) + Fe
2O
3 (s)  3 Na
2O (s) + 2 Fe (s)
–The numbers preceding the chemical formulae are
coefficients. They are used to balance the reaction.
–The numbers within the chemical formulae are
subscripts.
–You can read the above balanced reaction as:
•“6 atoms of solid sodium plus 1 formula unit of solid
iron (III) oxide yields 3 formula units of solid sodium
oxide and 2 atoms of solid iron” or…
•“6 moles of solid sodium plus 1 mole of solid iron (III)
oxide yields 3 moles of solid sodium oxide plus 2
moles of solid iron”
•Chemical reactions can never be read in terms of
grams, only in terms of particles or groups of particles
(moles).

5. TYPES OF CHEMICAL
REACTIONS

6. 1) COMBUSTION REACTIONS
a)All involve oxygen (O
2
) as a reactant,
combining with another substance
b)All combustion reactions are are
exothermic
c)Complete combustion of a
hydrocarbon always produces CO
2
and H
2O
d)Incomplete combustion of a
hydrocarbon will produce CO and
possibly C
(black carbon soot) as well
Ex: CH
4
+ 2O
2
=> CO
2
+ 2H
2
O (complete combustion – blue flame)
Ex: CH
4
+ 1.5O
2
=> CO + 2H
2
O (incomplete combustion – yellow flame)
Ex: CH
4
+ O
2
=> C + 2H
2
O (incomplete combustion – yellow flame, soot)

7. Combustion (cont’d)
•Any synthesis reaction which involves O
2
as a
reactant is also considered to be a combustion
reaction!
Ex. 2Mg + O
2
 2MgO
(metal oxide)
This is called the combustion of magnesium or
the synthesis of magnesium oxide. The
combustion of a metal always produces a metal
oxide (in this case, magnesium oxide). Make
sure the metal product is criss-crossed
correctly!

8. Two or more simple substances
(the reactants) combine to form
a more complex substance (the
product).
2) SYNTHESIS REACTION
Ex: 2Mg + O
2
 2MgO

9. SYNTHESIS REACTION
Types of synthesis:
a)Element A + Element B Compound
Na(s) + Cl
2 (g)  2NaCl(s)
a)Element + Compound A  Compound B
O
2(g) + 2SO
2(g)  2SO
3(g)
a)Compound A + Compound B  Compound C
CaO(s) + H
2
O(l)  Ca(OH)
2
(s)

10. Synthesis Reactions (cont’d)
•Metallic and nonmetallic elements react to form ionic
compounds. The resultant compound should be charge
balanced by the criss-cross method.
Ex. 4Li + O
2  2Li
2O
•Nonmetals react with each other to form covalent (molecular)
compounds. You should be able to draw a valid Lewis
Structure for the product.
2H
2
+ O
2
 2H
2
O
or
H
2
+ O
2
 H
2
O
2
But NOT
H
2 + O
2  2OH

11. A more complex substance (the
reactant) breaks down into two
or more simple parts (products).
Synthesis and decomposition
reactions are opposites.
3) DECOMPOSITION REACTION
Ex: 2H
2O  2H
2 + O
2
Electrolysis of
Water

12. DECOMPOSITION REACTIONS
(Cont’d)
Decomposition of a compound produces two or
more elements and/or compounds
The products are always simpler than the
reactant.
Gases are often produced (H
2
, N
2
, O
2
, CO
2
, etc.)
in the decomposition of covalent compounds.
Ionic compounds may be decomposed into pure
elements by using electricity (electrolysis). This is
how pure metals are obtained from salts.

13. The Decomposition of Water by
Electrolysis
2H
2
O  2H
2
+ O
2
An electrical
current can be
used to chemically
separate water into
oxygen gas and
hydrogen gas.
Notice that twice
as much hydrogen
is produced
compared to
oxygen!

14. 4) Single Replacement Between
Metals and Water
•Some metals have a higher activity than hydrogen
and can replace it in a single replacement
reaction. In these reactions, you may think of
water (H
2O) as H(OH).
•Ex: Na + H
2O  ?
Na + HOH  ?
Na + H
+
OH
-
 Na
+
OH
-
+ H

2Na + 2H
2O  2NaOH + H
2

15. Parts of two
aqueous ionic
compounds switch
places to form two
new compounds.
There are two
reactants and two
products.
5) DOUBLE REPLACEMENT
REACTION
Example:
AgNO
3
+ NaCl 
AgCl + NaNO
3

16. Double Replacement Reactions
The general form of a double replacement reaction is:
AB + CD  AD + CB
Just like single replacement reactions, not all double
replacement reactions actually occur.
We can experimentally attempt a D.R. reaction. The
reaction occurs if:
1)A solid precipitate is produced, or
2)A gas is produced, or
3)Water is produced.
If none of the above are produced and both products are
(aq), then there is no reaction (NR)!

17. Examples of Double Replacement
Reactions:
Pb(NO
3)
2 (aq) + 2NaI (aq)  PbI
2 (s) + 2NaNO
3 (aq)
(precipitate forming)
HCl (aq) + NaOH (aq)  NaCl (aq) + H
2
O (l)
(water-forming, acid-base, neutralization)
CaCO
3
(s) + 2HCl (aq)  CaCl
2
(aq) + H
2
CO
3
(gas-forming)

H(OH)
H
2
O (l) + CO
2
(g)

18. CLASSIFY THE FOLLOWING
REACTIONS INTO DIFFERENT TYPES
1) C
4
H
8
+ 6O
2
 4CO
2
+ 4H
2
O Combustion rxn
2) HCl + NaOH  H
2O + NaCl Double displacment rxn
3) 2KNO
3(s)  2KNO
2(s) + O
2(g) ...................................
4) 2Ag + S  Ag
2S ...................................
5) MgCO
3
(s)  MgO(s) + CO
2
(g) ...................................
6) Cl
2 + 2KBr  2KCl + Br
2 ...................................

19. Check Your Answers…
1)Combustion (of a hydrocarbon)
2)Double replacement (water forming)
3)Decomposition
4)Synthesis
5)Decomposition
6)Single Replacement