CHEMICAL REACTIONS AND EQUATIONS
Definitions
A. Chemical Reaction - The changing of one or more pure substances
into one or more new substances
B. Chemical Equation - A shorthand way of describing chemical
change, using symbols and formulas to
represent elements and compounds
C. General Form of an Equation:
REACTANT (S) ----------------> PRODUCT (S)
C
1 atom
of carbon
+
O2
1
molecule
of oxygen
-------------->
CO2
1 molecule
of carbon
dioxide
Formulas for reactants and products must be correct
C
+
O2
-----------------> CO2
carbon dioxide
C
+
O2
-----------------> CO
carbon monoxide
A reminder: Certain elements must always be written in their
diatomic forms.
N2, H2, O2, F2, Cl2, Br2, I2
Equations must be balanced by mass. ( The number of reactant atoms
of each element must equal the number of product atoms of each element.)
1.
C
2C
2.
+
O2 ------------------->
+
O2 ------------------->
N2 +
N2
+
H2 ------------------->
3H2
------------------->
CO
2CO
NH3
2NH3
Symbols Associated with Chemical Equations
1. (s) solid
(l) liquid (g) gas
2.
solid formed in the reaction
3.
gas formed in the reaction
4. (aq)
Indicates an aqueous solution
General Rules for Balancing Equations
1. Balance elements other than H, O, and polyatomic ions
(which do not change in the equation)
Generally, start with the element that appears the most.
2. Balance the polyatomic ions
3. Balance the H atoms
4. Balance the O atoms
}*
5. Check the coefficients for the lowest whole number ratio
* You may have to back up after
each of these steps if the results
of a previous step are changed
Examples of the “Balancing” Process
P4
P4
P4
Al
2 Al
2 Al
4 Al
+ H2
+ H2
+ 6 H2
+
O2
+
O2
+ 3 O2
+ 3 O2
---------->
PH3
----------> 4 PH3
----------> 4 PH3
-------------------->
Al2O3
-------------------->
Al2O3
--------------------> 2 Al2O3
--------------------> 2 Al2O3
V
2 V
2 V
4 V
+
O2
+
O2
+ 5 O2
+ 5 O2
---------->
---------->
---------->
---------->
2
2
V 2 O5
V 2 O5
V 2 O5
V 2 O5
KClO3 ------------------->
KClO4 + KCl
2 KClO3 ------------------->
KClO4 + KCl
4 KClO3 -------------------> 3 KClO4 + KCl
H2SO4
H2SO4
H2SO4
+
NaCN
+ 2 NaCN
+ 2 NaCN
---------->
---------->
---------->
Na2SO4
Na2SO4
Na2SO4
+
HCN
+
HCN
+ 2 HCN
H3PO4
H3PO4
2 H3PO4
2 H3PO4
+
Ca(OH)2
+ 3 Ca(OH)2
+ 3 Ca(OH)2
+ 3 Ca(OH)2
---------->
---------->
---------->
---------->
CH4 +
O2 --------------->
CH4 +
O2 --------------->
CH4 + 2 O2 --------------->
C3H8
C3H8
C3H8
C3H8
+
+
+
+ 5
O2
O2
O2
O2
Ca3(PO4)2
Ca3(PO4)2
Ca3(PO4)2
Ca3(PO4)2
+
+
+
+ 6
H 2O
H 2O
H 2O
H 2O
CO2 +
H 2O
CO2 + 2 H2O
CO2 + 2 H2O
---------->
CO2
----------> 3 CO2
----------> 3 CO2
----------> 3 CO2
+
H 2O
+
H 2O
+ 4 H 2O
+ 4 H 2O
C 2H2
C 2H2
+
+
O2
O2
---------->
CO2
----------> 2 CO2
+
+
H 2O
H 2O
+
O2
+ 5 O2
----------> 4 CO2
----------> 4 CO2
+
+
H 2O
H 2O
?
2 C2 H 2
2 C2 H 2
Fe
Fe
2 Fe
4 Fe
4 Fe
+ O2
+ O2
+ ? O2
+ ? O2
+ 3 O2
+
+
+
+
+
3
3
6
6
H 2O
H 2O
H 2O
H 2O
H 2O
------------------->
------------------->
------------------->
------------------->
------------------->
2
2
4
4
Fe(OH)3
Fe(OH)3
Fe(OH)3
Fe(OH)3
Fe(OH)3
Classification of Reactions
Combination Reactions
+
4 Al (s) + 3 O2 (g)
2 H2 (g) + O2 (g) --------->
C2H4 (g) + H2O2 (aq)
2 Al2O3 (s)
2 H2O (g)
C2H6O2 (l)
2H2+ O2 ---> 2H2O
Decomposition Reactions
+
2 HgO (s) --------->
2 Hg (l) + O2 (g)
CaCO3 (s) ---------> CaO (s) + CO2 (g)
2 NaCl (s) --------->
Cl2 (g) + 2 Na (l)
Single Replacement Reactions
+
+
Cu (s) + 2 AgNO3 (aq) ---------> 2 Ag (s) + Cu(NO3)2 (aq)
2 Al (s) + Fe2O3 (s) ---------> Al2O3 (s) + 2 Fe (l)
Mg (s) + 2 HCl (aq) ---------> H2 (g) + MgCl2 (aq)
Double Replacement Reactions
+
+
Ba(NO 3)2 (aq) + Na2SO4 (aq) ---------> BaSO4 (s) + 2 NaNO 3 (aq)
PCl3 (l) + 3 AgF (s) ---------> PF3 (g) + 3 AgCl (s)
HCl (aq) + NaOH (aq) ---------> H2O(l) + NaCl (aq)