Chemical
RXNs
SIGNS OF CHEMICAL RXNS
Color change - new substances might reflect
different colors of light.
Heat change - the container may get hotter
or colder.
Gas produced - bubbles or smoke may be
observed.
Precipitate formed - an insoluble solid might
form in a liquid.
CONDITION FOR A
CHEMICAL RXN:
•reactants have ability to form
chemical bonds.
•Bonds are formed by valence
electrons of reactant atoms.
“If valence electrons of
substances brought
together do not match to
complete the Octet Rule,
there will be no chemical
reaction”.
Parts of a rxn:
Reactants
•Substances that interact with each
other; left side of the arrow in a chemical
equation.
Products
•New substances formed during a
reaction; right side of the arrow in a
chemical equation.
Reactants
Products
TYPES OF CHEMICAL
REACTIONS
A +B
C
C
A + B
FORM
SEPARATE
SWITCH 1
A + BX
AX + B
AX + BY
AY + BX
SWITCH 2
Chemical reaction types:
synthesis, decomposition,
single replacement, double
replacement, and
combustion.
Synthesis: two simple
substances combine to form a
more complex one.
Example:
element + element
A +
B
compound
C
2Na + Cl2
4Fe + 3O2
2NaCl
2Fe2O3
REACTION OF COPPER POWDER
•WORD EQUATION
•CHEMICAL EQUATION
•BALANCED CHEMICAL
EQUATION
REACTION OF COPPER POWDER
2Cu + O2
(2CuO)
Copper Oxide
(2CuO)
Pesticide
Fungicide
TYPES OF CHEMICAL
REACTIONS
A +B
C
C
A + B
FORM
SEPARATE
SWITCH 1
A + BX
AX + B
AX + BY
AY + BX
SWITCH 2
Chemical reaction types:
synthesis, decomposition,
single replacement, double
replacement, and
combustion.
Synthesis: two simple
substances combine to form a
more complex one.
Example:
element + element
A +
B
compound
C
2Na + Cl2
4Fe + 3O2
2NaCl
2Fe2O3
REACTION OF COPPER POWDER
•WORD EQUATION
•CHEMICAL EQUATION
•BALANCED CHEMICAL
EQUATION
REACTION OF COPPER POWDER
2Cu + O2
(2CuO)
Copper Oxide
(2CuO)
Pesticide
Fungicide
Decomposition: a complex
substance breaks down into
two simple substances.
compound
C
2H2O
H2CO3
element + element
A
+
B
2H2 + O2
H2O + CO2
Lab: Separating
Water
What will happen to water when an electric
current is allowed to run through it?
MAKING OBSERVATIONS
What predictions
can you make based
on the given
information?
• What
do you think will happen when water separates?
• What do you expect to observe during the separation?
• Is there a way to identify hydrogen? oxygen?
• What
do you know about H and O2? What phase of matter
will they exist?
2H2O --> 2H2 + O2
Single replacement:
a
single element replaces an element in
a compound.
element + compound
Zn + 2HCl
2Na + 2H2O
compound + element
ZnCl2 + H2
2NaOH + H2
SINGLE REPLACEMENT:
Reaction of Metals (Mg, Al, FE, Cu, Zn) to HCl
Metal
Word/Chemical Equation
Zinc
Zn + 2HCl  H2 + ZnCl2
Iron (II)
Magnesium
Aluminum
Chemical
Equations
1 WORD EQUATION
Copper oxide (ore)
plus hydrogen gas
produce copper
metal plus water
2 CHEMICAL EQUATION
CuO + H2  Cu + H2O
Coefficient
5H2
Subscript
Element
BALANCED EQUATION
+
-->
Reactants
Products
Reactants
Products
CuO + H2 --> Cu + H2O
BALANCED EQUATION
1 copper
1oxygen 2
hydrogen
1 copper 2
hydrogen
1 oxygen
BALANCED EQUATION
+
-->
Reactants
Products
Reactants
Products
2 H2 + O2 -->
BALANCED EQUATION
Reactants
Products
__H2 +__ O2 -->
__H2O
BALANCED EQUATION
Reactants
Products
2 H2 + O2 --> 2 H2O
BALANCED EQUATION
4 hydrogen 2
oxygen
4 hydrogen
2 oxygen
Chemical Equation:
2 H2 + O2 --> 2 H2O
a
way to represent chemical
reactions on paper.
Law of conservation of
mass:
“During a chemical rxn, atoms are
neither created nor destroyed. The
number of atoms remains constant
throughout the reaction. Since the
number of atoms doesn't change, the
mass must remain constant as well”.
There are times when mass might
appear to change during a
chemical reaction. If you
experience this during an
experiment, be sure to remember
the law of conservation of mass.
The change in mass must be
accounted for in a way other than
destroying or creating atoms.
Equations must be
balanced because:
Atoms can be neither created nor
destroyed in an ordinary chemical
reaction, so there must be the
same number of atoms on both
sides of the equation.
Balance equations by
changing coefficients
never by changing formula
subscripts
Interactive Tutorials on
Balancing Equations
Click on this site:
GenChem - Balance Equation
http://www.wfu.edu/~ylwong/balanceeq/balanceq.html