Section 2.6—Chemical
Reactions
If we’re going to do chemical reactions with antacids, we’d better know how to write
them!
Chemical Reactions
Bonds and atoms are rearranged to
form new compounds.
2 H2 + O2  2 H2O
O
O
Watch as 2 H2 and 1 O2 undergo a chemical reaction
Chemical Reactions
Bonds and atoms are rearranged to
form new compounds.
2 H2 + O2  2 H2O
O
O
The compounds in the end are different from those in the beginning
Bonds are broken and formed between different atoms
Chemical Equations
The “sentence” of chemistry that shows
how the starting materials and the final
products of a chemical reaction
Examples of Chemical Equations
Word equation: magnesium metal is reacted with
aqueous hydrochloric acid to produce aqueous
magnesium chloride and hydrogen gas
Formula equation: Mg (s) + 2 HCl (aq)
MgCl2 (aq) + H2 (g)
Visualization
H
Cl
Mg
Cl
H
Cl
Mg
Cl
H H
Parts of a Chemical Equation
The starting materials
for the reaction—each
compound is
separated by a “+”
Formed in the
reaction
Products
Reactants
NaCl (aq) + AgNO3 (aq)  AgCl(s) + NaNO3 (aq)
States of matter
Arrow
s = solid
l = liquid
g = gas
aq = aqueous
(dissolved in water)
Read as:
Yields
Produces
Forms
Makes
etc.
Writing Chemical Equations
You must write each chemical formula
correctly first! (Section 2.2)
“and”, “is mixed with” or “reacts with” = +
“yield”, “produces” and “forms” = 
We will learn to balance equations in the next section, so
don’t worry about it now!
Let’s Practice #1
Example:
Write the word
equation into
symbol form
Aluminum metal is reacted with
hydrochloric acid to form
aluminum chloride and hydrogen
gas
Let’s Practice #1
Example:
Write the word
equation into
symbol form
Aluminum metal is reacted with
hydrochloric acid to form
aluminum chloride and hydrogen
gas
Al + HCl  AlCl3 + H2
Let’s Practice #2
Example:
Write the word
equation into
symbol form
Copper (II) nitrate and sodium
hydroxide form copper (II)
hydroxide and sodium nitrate
Let’s Practice #2
Example:
Write the word
equation into
symbol form
Copper (II) nitrate and sodium
hydroxide form copper (II)
hydroxide and sodium nitrate
Cu(NO3)2 + NaOH  Cu(OH)2 + NaNO3
Double Replacement Reactions
The cations from two compounds replace
each other.
NaCl + AgNO3  AgCl + NaNO3
Two ionic compounds switch ions
Double Replacement Reactions
General format of a double replacement reaction:
A
X
B
Z
A
Z
B
X
Products of a Double Replacement
1
CaCl2
Combine the cation of the first reactant with the anion of the
second reactant
+ AgNO3
Products of a Double Replacement
2
CaCl2
Combine the cation of the second reactant with the anion of the
first reactant
+ AgNO3
Products of a Double Replacement
3
Remember to write cations first …
& balance charges with subscripts when writing formulas
Only leave subscripts that are in the original compound
there if they are a part of a polyatomic ion!
CaCl2
CaCl2
+ AgNO3
+
AgNO3
Ca(NO3)2
+
AgCl
Neutralization Reactions
General format of a neutralization reaction:
H
X
B
O
H
B
X
O
H
Neutralization reactions are double replacement reactions
where one cation is “H” and one anion is “OH” and water
is formed
H
Products of a Neutralization Reaction
1
H2 SO4
Combine the cation of the first reactant with the anion of the
second reactant
+ Na OH
Products of a Neutralization Reaction
2
H2 SO4
Combine the cation of the second reactant with the anion of the
first reactant
+ Na OH
Products of a Neutralization Reaction
3
Remember to write cations first …
& balance charges with subscripts when writing formulas
Only leave subscripts that are in the original compound
there if they are a part of a polyatomic ion!
H2 SO4
H2 SO4
+ Na OH
+
Na OH
Na2SO4
+
HOH
You can write the water as “HOH” when you combine the cation & anion
or you can change it to “H2O”
Let’s Practice #3
Example:
Write the
products for
this reaction
Sr(OH)2 + HBr 
Let’s Practice #3
Example:
Write the
products for
this reaction
Sr(OH)2 + HBr 
SrBr2 + HOH
Let’s Practice #4
Example:
Write the
products for
this reaction
HCl + Ca(OH)2 
Let’s Practice #4
Example:
Write the
products for
this reaction
HCl + Ca(OH)2 
CaCl2 + HOH