a shorter, easier way to show chemical reactions, using
symbols, not words, for the reactants and the products
hydrogen molecules react with oxygen molecules to form water molecules
H2
+
O2
H2O
reactant + reactant “YIELDS” products
total mass of reactants must equal total mass of products
matter is NOT destroyed or created in a chemical reaction
=
ELEMENTS – represented by a one or two-letter symbol (letter)
C
Na
H
COMPOUNDS– represented by a chemical formula (word) which
uses subscripts to show the ratio of elements in the compound
H2O2
CO2
C3H8O
HOW MANY?
coefficient in front of the chemical formula tells “how many” atoms or molecules
3H2O2
4CO2
2C3H8O
•
Add the subscript “2” to all diatomics that are
ALONE in the equation (N, O, F, Cl, Br, I, H)
(note: only time a subscript can & must be changed)
•
Count the number of atoms that are present in
the basic equation and record
•
Pick an element that is not balanced on both
sides of the equation ( H & O last)
•
Add a coefficient in front of the chemical
formula to adjust the count and record the
new values
•
Continue adding coefficients to obtain the
same number of atoms of each element on
both sides of the equation
(change coefficient, then change counts)
H + O
H2O
•
Add the subscript “2” to all diatomics that are
ALONE in the equation (N, O, F, Cl, Br, I, H)
Mg + O
MgO
(note: only time a subscript can & must be changed)
•
Count the number of atoms that are present in
the basic equation and record
•
Pick an element that is not balanced on both
sides of the equation ( H & O last)
•
Add a coefficient in front of the chemical
formula to adjust the count and record the
new values
•
Continue adding coefficients to obtain the
same number of atoms of each element on
both sides of the equation
(change coefficient, then change counts)
C
+
Cl
CCl4
Mg
C
+
+
O2
Cl2
------>
------>
MgO
CCl4
Al
+
O2
Al2O3
Note: add like elements on the same side of the equation
SO2 +
O2
SO3
•
Add the subscript “2” to all diatomics that are
ALONE in the equation (N, O, F, Cl, Br, I, H)
Al
+
O
Al2O3
SO2 + O
SO3
(note: only time a subscript can & must be changed)
•
Count the number of atoms that are present in
the basic equation and record
•
Pick an element that is not balanced on both
sides of the equation ( H & O last)
•
Add a coefficient in front of the chemical
formula to adjust the count and record the
new values
•
Continue adding coefficients to obtain the
same number of atoms of each element on
both sides of the equation
(change coefficient, then change counts)
SYNTHESIS – two or more substances combine to make a more complex substance
AB
2 SO2
+
+
O2
+
C
ABC
2 H2O
(synthesize means to put together)
2 H2SO4
Synthesis of Acid Rain
DECOMPOSTION - a complex substance breaks down into simpler substances
ABC
AB
2 H2O2
2 H2O
+
C
+
(decompose means to break down)
O2
Decomposition of Hydrogen Peroxide
REPLACEMENT – two elements in two different compounds trade places
AB
+
2 CuO
CD
+
C
AC
2 Cu
+
BD
+
CO2
(replace means to find a new partner)
Isolating Copper by Replacement