Download Chemical reactions and equations

CHEMICAL REACTIONS AND
EQUATIONS
SLO 4/27/16
Students will be able to interpret chemical
equations based on their reactants and products.
What do we know about equations?

From Math:

In Chemistry:
Equations

Chemical equations used to represent chemical
reactions where the beginning substance(s) is changed
into a new substance(s)
Reactions start with Reactants on the left side of the
equation.
 Reactions end with Products on the right side of the
equation.
 An arrow in between the Reactants and Products is called the
Yield sign and acts almost like an equal (=) sign in math.

 Reactant(s)
 Product(s)
3 Ways to represent equations:
Word equations- the reaction is written out with
words and symbols
 Skeleton equations- the reaction is written out
using formulas and symbols but amounts of each
substance are not specified (kind of like a
recipe without measurements)
 Balanced chemical equations- the reaction is
written out using formulas and symbols.

 Amounts
of each substance are specified (like a
recipe with measurements)
Writing word equations
1) Write the names of the reactants to the left of the
arrow separated by plus signs
2) Draw the arrow
3) Write the names of the products to the right of the
arrow, also separated by plus signs

Remember to use the proper naming system for ionic
compounds, covalent compounds, and acids
11.1
Examples of word equations
 iron
+ oxygen  iron(III) oxide
11.1
Examples of word equations
 Hydrogen
Peroxide  Water and Oxygen
11.1
Examples of word equations
 Methane
+ Oxygen  Carbon dioxide + Water
Writing Skeleton Equations



1) Write the formulas of the reactants using element
symbols to the left of the yield sign (arrow)
2) Draw the arrow
3) Write the formulas of the products to the right.
 Sometimes
symbols are used to indicate states of matter,
however, skeleton equations often lack this information
Skeleton Equations
The skeleton equation for the rusting of iron is:


The skeleton equation for the decomposition of
hydrogen peroxide is:


Fe + O2  Fe2O3
H2O2 H2O + O2
The skeleton equation for the reaction of methane
and oxygen is:

CH4 + O2  CO2 + H2O
Writing Balanced Equations
1)Determine correct formulas for reactants and
products
 Pay
attention to ionic vs. covalent naming!
2) Write skeleton equation using the formulas for
reactants and products
3) Add any symbols needed for state of matter,
catalysts, heat, etc.
4) Count the number of atoms of each element.
 Include
any polyatomic ion that occurs on both
sides as a single unit- as if they were one element
Writing Balanced Equations
5)
Balance elements one at a time by changing
coefficients.
 Begin
with those that occur only once on each side.
Water and oxygen should often be done last.
 DON’T CHANGE SUBSCRIPTS!!!! (changing the
subscript changes what the reactant or product is!)
6) Check your work- count up number of atoms on
each side- they should be the same
7) Make sure all coefficients are in the lowest
possible ratio
Balanced Equations
The balanced equation for the rusting of iron is:


The balanced equation for the decomposition of
hydrogen peroxide is:


4Fe + 3O2  2Fe2O3
2H2O22H2O + O2
The balanced equation for the reaction of methane
and oxygen is:

CH4 + 2O2  CO2 + 2H2O
11.1
Terms to know:
 Coefficient-
the large number that is written in front
of the formula of a substance
 A catalyst is a substance that speeds up the
reaction but is not used up in the reaction.
Without Catalyst
With Catalyst
Symbols you will use when you write your
final balanced equation
Classwork!

Reading Assignment: Chapter 11.1

Written Assignment: pg. 354, #7, 8, and 10
Practice Worksheet on Reactions!


Work on the practice worksheet to solve various
chemical reaction problems that we have covered
so far.
This worksheet will count as a classwork grade and
will be collected when you are finished.
Exit Slip


What are the three ways that chemical equations
can be written and give an example of each:
Make sure I get your slip before you leave; this
counts as part of your participation grade!