Do Now: (this problem is in your
packet)
Ribose is an important sugar found in DNA and
RNA. Ribose has a gram molecular mass of
150 g/mol and an empirical formula of CH2O.
What is the molecular formula for ribose?
Chemical Equations
What are they?
Def: represents, with symbols and formulas,
the reactants and products of a chemical
reaction
• Details the ratios of the substances that react.
• Equation must contain the correct formulas of
reactants and products
Law of Conservation of Mass
• matter cannot be created or destroyed
• same # of atoms of each element must
be written as products and reactants
• coefficients are written to equalize the
number of atoms of each element
(coefficients – numbers placed before
chemical formulas)
Balancing chemical equations
1. Identify the names of reactants and products.
Ex) Sodium metal reacts with chlorine gas to form
sodium chloride
Sodium + Chlorine  sodium chloride
2. Substitute the correct symbols and formulas
Na (s) + Cl2 (g)  NaCl (s)
Keep it going!
3. Balance the number of atoms of each
element by changing coefficients only!
• subscripts MAY NOT be changed for a chemical,
this will change the identity of the substance
___Na (s) + ___Cl2 (g)  ___ NaCl (s)
4. count the number of atoms of each element
to be sure the equation is balanced.
Helpful Hints
• When polyatomic ions appear the same on
both sides of the equation, count them as only
one item
When water is formed or decomposed from
hydrogen and a hydroxide ion, write the
water in as HOH
Example
Aluminum + hydrogen nitrate  Aluminum nitrate + hydrogen
Example
Na +
H2O
 H2 +
NaOH
Example
MgCl2 +
Na2CO3 
MgCO3 + NaCl
Types of Chemical
Reactions
1. Synthesis Rxns (combination) – two or
more substances combine to form a single
new substance
General formula: A + B → AB
Synthesis Reaction
Examples
Mg(s) + O2(g)  MgO(s)
Na(s) + S(l) 
CaO(s) + H2O(l) 
SO3(g) + H2O(l) 
2. Decomposition
Def: a single compound is broken down into
two or more products
General formula: AB → A + B
Decomposition Reaction
Examples
[electrolysis]
electricity
H2O (l)  H2(g) + O2(g)
electricity
NaCl (l)

Decomposition Reaction
Examples
Decomposition of carbonates
Heat, D
CaCO3(g)  CaO(s) + CO2(g)
heat
Sodium carbonate

Decomposition Reaction
Examples
Decomposition of metal hydroxides
heat
Mg(OH)2(s)
heat
Ba(OH)2


MgO(s) + H2O(l)
Decompostion of metal chlorates
heat
NaClO3(s) 
NaCl(s) + O2(g)
heat
KClO3

3. Single Replacement
RXNS
Def: one element replaces a second element in
a compound
• metals replace metals
• nonmetals replace nonmetals
General Formula: A + BC → AC + B
How does it work?
• check Table J – Activity series
• more active metals replace less active metals
• (elements can only replace other elements
that are lower on Table J)
• more active nonmetals replace less active
nonmetals
Metals replacing less active metals
Mg(s) + Zn(NO3)2(aq)  Mg(NO3)2(aq) + Zn(s)
Zn(s) + AgNO3(aq) 
Zn(s) + CaSO4 
Replacement of halogens
Cl2(g) + KI(s) 
I2(s) + NaF 
Replacement of H in water by a metal
K(s) + H2O 
Replacement of hydrogen in an acid by a metal
Zn(s) + HCl(aq) 
4. Double replacement
reactions
Def: involves the exchange of positive ions
between two reacting aqueous compounds
General Formula: AB + CD → AD + CB
products typically include:
• a precipitate (nearly insoluble compound)
• an insoluble gas (bubbles out of solution)
• a molecular compound (usually water)
Examples
Pb(NO3)2(aq) + KI(aq)  PbI(s) + 2KNO3(aq)
FeS(s) + HCl 
NaCl + AgNO3 
HNO3 + KOH 
Predict the products and
Balance this puppy!
Ba(OH)2 + H3PO4 →
5. Combustion Rxns
Def: an element or a compound reacts with
oxygen producing heat and light
hydrocarbons burn completely to form water
and carbon dioxide
Examples
C2H6(g) + O2(g) 
C8H18 + O2 
Mass Relationships in Chemical
Reactions
• Stoichiometry is the term used to describe the
mass relationships in chemical reactions.
The coefficients in a balanced chemical equation
represent the mole to mole ratio of the reactants
and products
• the relative amount of reactant needed or
product formed in a chemical reaction can be
determined by stoichiometry (the equation acts
like a recipe for the reaction that takes place)
N2 + H2 → NH3
After balancing the equation, how many moles
of H2 are consumed in the reaction? ____
How many moles of NH3 are produced? _____
Therefore, there is a ______ : _______ ratio of
H2 to NH3.
Calculating the # of moles consumed or
produced according to a chem equation:
1. Balance the equation.
2. Write the given quantity from the question
above that substance in the equation. Place
an X above the substance that you are trying
to find.
3. Establish a ratio of the given quantity to the
balanced coefficient for each substance in
question.
4. Cross multiply to solve for X.
N2 + H2 → NH3
If 2 moles of N2 react completely:
a. How many moles of hydrogen must react?
b. How many moles of ammonia will be
produced?
C2H6 +
O2 
CO2 +
H2O
a. How many moles of CO2 are produced when
1 mole of ethane (C2H6) is consumed?
b. How many moles of O2 are consumed when 5
moles of water are produced?
The following balanced equation
shows the complete combustion of
octane.
Gasoline is a complex mixture of many
chemicals.
For the purpose of this calculation, we
will assume that gasoline is comprised
entirely of a compound called octane.
2 C8H18 + 25 O2 → 16CO2 + 18H2O
2 C8H18 + 25 O2 → 16CO2 + 18H2O
• How many moles of octane (C8H18) are there
in 10.0 gallons (26,714g)?
2 C8H18 + 25 O2 → 16CO2 + 18H2O
• Use the balanced equation to determine how
many moles of CO2 are produced when all of
the octane in the previous question is
completely consumed?
When 2.0 mol of octane are
burned 10943 kj of heat are
produced. How many grams of
water at 100 degrees Celsius can
be boiled?