# Stoichiometry

In this unit we move up from writing words (chemical formulas) to
writing
sentences and maybe even paragraphs (chemical reactions). Of
course
writing sentences means that one must be able to write words so in the
study
of chemistry one must be able to write formulas before attempting to
write
equations for chemical reactions.

Stoichiometry is simply a fancy word for calculating amounts (grams,
moles,
liters) in chemical reactions. The key part of this process is
understanding
the the mole relationships in the chemical equation. This
involves
balancing a chemical equation as the first step.

The process of **balancing a chemical equation** is a
subset
of a basic scientific principal of the Law of Conservation of Matter.
This
law states that matter is neither created or destroyed (or matter is
conserved
in all non nuclear reactions). In chemistry we demonstrate this
by
writing balanced equations. A balanced equation is simply one
where
the number of each kind particle on each side of the equation is the
same.
The first step in writing a balanced equation is to write a
skeleton
equation, one with correct formulas for reactants
(on the left side of the arrow) and products
(on the right side of the arrow). Then one needs to change the
number
of particles on each side until they are all equal. We do this by
putting
coefficients in front of the correct
formulas
(we do **NOT** change the formulas).

Once the equation is balanced, the stoichiometry part is possible.
This
is because **the coefficients of the
balanced
equation give the mole ratios of the compounds**.
This
is why we spent so much time in the last unit on moles. **The mole is the "super secret unit" of chemistry**
because almost all of the calculations that are done in chemistry
involve
moles. If one can find the number of moles of a reactant or
product
then it is only one simple additional step of using the coefficients of
the
balanced equation to calculate the moles of anything else in the
equation.
Using this process one can for example, calculate the volume of
oxygen
necessary to "burn" 120 grams of sugar when it is eaten.

**Unit VII Chemical Reactions**

Be able to predict synthesis, single replacement, double replacement,
decomposition
and combustion reactions.

Be able to balance chemical reactions, including redox reactions

Be able to calculate mass, mole, and volume relationships in chemical
reactions
(Stoichiometry).

**Terms:** chemical reaction, reactant, product, single
displacement,
double displacement, decomposition, synthesis, combustion,
stoichiometry,
mass-mass problem, mass-mole problem, mass-volume problem,
oxidation,
reduction, oxidizing agent, reducing agent.

Suggested Problems: Read Chapter 9 and Chapter 25

pgs 243-247 (43-46, 48-55, 58-61) Review (1-12)

pgs 646-647 (39, 43, 45-47, 49, 50)

Return to the HHS Science Home Page
# Links

The
Chemical
Reaction Page

ChemTeam: Stoichiometry

Fundamentals
from UNC, Chapel Hill

Problem
solving strategies

On the ChemTeam site there is a Stoichiometry Worksheet (#3 under Lab Experiments
& Worksheets). There are 10 Stoichiometry problems here. I
will give you 1 extra credit point for each correctly worked problem.