An Intro. To Chemical
Reactions
What is a chemical reaction?
How do we represent chemical reactions?
Chemical Reactions
 Chemical Reaction: the change of one or
more substances by the breaking of bonds in
the reactants and the formation of new bonds
to form products; new substances formed.
 Reactants: substances undergoing reaction
 Products: New substances formed
 Catalyst: a substance that speeds up the rate
of a reaction but is not used up in reaction;
shown on arrow
Evidence of a Chemical Reaction
 Production of a gas/bubbles
 A solid (precipitate) forms
 Color changes
 Energy is released (light, flames,
heat, etc.) or absorbed
An Example of a Chemical
Reaction
Photosynthesis:
 Word Equation:
Carbon dioxide gas + liquid water with
sunlight produces oxygen gas + solid
glucose
An Example of a Chemical
Reaction cont’
 Skeleton Equation:
CO2(g) + H2O(l)
O2(g) + C6H12O6(s)
 Balanced Chemical Equation
6CO2(g) + 6H2O(l)
6O2(g) + C6H12O6(s)
Guidelines to Writing Skeleton
Equations:
1. From the problem, write a word equation.
Determine which substances are reactants
and products and where the  (“yields”)
symbol should be placed.
b. Include states of matter for all substances.
Example: Making Rust
A piece of solid iron is combined with oxygen
gas to form solid iron (III) oxide.
Solid iron + oxygen gas  solid iron (III) oxide
a.
Guidelines to Writing Skeleton
Equations:
2. Write the chemical formula for all reactants
and products – 5 Situations
Single Elements – write the symbol for element
w/o a subscript.
Example: Aluminum metal
Al(s)
b. Diatomic Element (7) - Write symbol for element
w/ a subscript of 2; Hydrogen, Nitrogen, Oxygen,
Fluorine, Chlorine, Bromine and Iodine
Example: Chlorine gas
Cl2(g)
a.
Guidelines to Writing Skeleton
Equations:
c.
Ionic Compound – Use crisscross method w/
ionic charges.
- No prefixes in name, contains a metal, polyatomic
ion or roman numeral
Example: Chromium (III) sulfite
Cr+3SO3-2 = Cr2(SO3)3
d. Molecular Compounds – Prefixes = Subscripts
- They will have prefixes in name and contain all
nonmetals.
Example: Disulfur trioxide
S2O3
Guidelines to Writing Skeleton
Equations:
e. Common Names: Look up formula in
textbook or other resource
Examples:
Hydrochloric acid – HCl(aq)
Methane gas – CH4(g)
Guidelines to Writing Skeleton
Equations:
3. Add abbreviations for state of each
substance after its formula.
(s) = solid
(l) = liquid
(g) = gas
(aq) = aqueous solution (a solid dissolved in
water)
Examples…
Write the chemical equation for the following word
equation:
Solid silver sulfide reacts with aluminum metal
to produce solid aluminum sulfide and silver
metal
Examples…
Write the chemical equation for the following
word equation:
Aqueous zinc hydroxide combined with
phosphoric acid forms solid zinc phosphate and
liquid water