Chemical
Reactions
Applied Chemistry
Chemical Reaction

Chemical reaction – The type of reaction
in which the properties of the reactants
are different from the products.

Chemical Change – A change that
produces new substances with new
properties and compositions.

Physical changes do NOT change the
identity of a substance.
 Nuclear changes involve changes to the
nucleus. Ex) fission and fusion
Signs of a chemical change

Change in color

Formation of a precipitate (cloudiness,
solid formed from 2 solutions)

Production of a gas (bubbles; fizzing)

Increase or decrease in temperature

Change or production of an odor
Chemical Equations

A description of a chemical reaction
using symbols instead of words.

Parts of a Chemical Equation:
A.
B.
C.
D.
Reactants
Products
Arrow
Plus Sign
Parts of Chemical Equation
A. Reactants
CH4 + O2  H2O + CO2
reactants
products

Written on the left side of the arrow

Starting material in a chemical reaction
Parts of Chemical Equation
B. Products
CH4 + O2  H2O + CO2
reactants
products

Written on the right side of the arrow.

Newly formed substances that are produced in a
chemical reaction.

Properties are different than those of the
reactants.
Parts of Chemical Equation
C. Arrow
CH4 + O2  H2O + CO2
reactants
products

Yield sign

Means yields or produces

Separates the reactants from the
products.
Parts of Chemical Equation
D. Plus sign
CH4 + O2  H2O + CO2
reactants

products
Used to separate reactants and to
separate products
Symbols for states
H2 (g) + O2 (g)  H2O (l)
KI(aq) + Pb(NO3)2 (aq)  PbI2(s) + KNO3(aq)
Physical states of the reactants and products are in
parenthesis beside the formula.

g:
gas

l:
liquid

s:
solid

aq: aqueous (dissolved in water)
Example Reaction
H2 (g) + Cl2 (g) → HCl (g)

What are the reactants?
H2 and Cl2

What are the products?
HCl

What is the physical state of all the
substances?
gas
Catalysts



Catalysts are sometimes added to
reactants to help speed up a chemical
reaction.
Catalysts are unchanged in a
chemical reaction. They are neither
reactants nor products.
Catalysts are written above the yield
sign.
MnO2
H2O2  H2O + O2
Law of Conservation of Mass





Mass is neither created nor destroyed in a
chemical reaction, it can only change form.
Mass of the reactants is the SAME as the mass of
the products.
The number of each type of atom in the reactants
must be equal to the number of atoms in the
products.
Since the number of atoms is the same, the mass
will be the same on both sides of the reaction.
Also, the types of elements will be the same on
each side.
Balancing Equations
H2 (g) + Cl2 (g) → HCl (g)
Reactant side
# of H atoms = 2
# of Cl atoms = 2

Product side
# of H atoms = 1
# of Cl atoms = 1
Does this equation have the same number of atoms
of each element on both sides of the equation?
NO!!!

Therefore, it does not follow the Law of
Conservation of Mass.
Balancing Equations (cont.)
H2 (g) + Cl2 (g) → HCl(g)

This equation is called a skeleton
equation.

This equation must be balanced with
coefficients (the number in front of a
formula for a substance).
a BALANCED Equation…
H2 (g) + Cl2 (g) → 2HCl(g)
Reactant side
# of H atoms = 2
# of Cl atoms = 2
Product side
# of H atoms = 2
# of Cl atoms = 2
A coefficient of 1(one) is understood and is not necessary in
the balanced chemical equation.
Steps for balancing equations
Write the chemical formula for each
reactant and product.
2. Indicate the state of each substance.
3. Use coefficients in front of the substance
to balance the equation. The number of
each atom should be the SAME on both
sides of the equation.
NOTE: NEVER CHANGE SUBSCRIPTS!!!
1.
Balancing Examples
1.
H2 + Br2 → 2HBr
2.
2Na + Cl2 → 2NaCl
3.
4Na + O2 → 2Na2O
4.
Zn + 2HCl → ZnCl2 + H2
5.
4Fe + 3O2 → 2Fe2O3
Balancing Examples
6.
P4 + 5O2 → 2P2O5
7.
Al2O3 + 3H2 → 2Al + 3H2O
8.
2Ca + O2 → 2CaO
9.
3Cl2 + 2AlBr3 → 3Br2 + 2AlCl3
10.
2HgO → 2Hg + O2
Synthesis Reactions

Two or more reactants produce ONE
product

A.K.A. Direct combination reactants

Follows the pattern: A + B → AB
**only ONE product**
N2 + 3H2 → 2NH3
2 reactants → 1 product
Synthesis Reaction
Combustion Reactions

Chemical reaction involving oxygen (O2) in
which light and heat are produced. Heat is
a useful product.

When fuels are burned in the presence of
oxygen, water (H2O) and carbon dioxide
(CO2) are often produced.

Follows the pattern: BC + A → BA + CA
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O(g) + heat
Combustion Reaction
Decomposition Reactions



Opposite of synthesis reactions
Substance breaks down into simpler
substances.
Chemists can cause decomposition, but
decomposition can also be spontaneous.
AB → A + B
Only ONE reactant!
2H2O → 2H2 + O2
1 reactant → 2 products
Single Displacement
(Replacement) Reactions
Change in bonds.
 One substance will replace, or bump out,
another element in a compound.

A + BC → AC + B
(2 reactants – element and compound
2 products – element and compound)
Zn + H2SO4 → ZnSO4 + H2
Double Displacement
(Replacement) Reactions

Both substances change partners
AB + CD → AD + CB
2KI(aq) + Pb(NO3)2 (aq)  2KNO3(aq) + PbI2(s)
2 reactants (both compounds) and
2 products (both compounds)
Energy Changes in Reactions
Exothermic Reactions

Release heat into the surroundings

Surroundings will get hotter.

Sometimes need heat to them started.

A noticeable increase in temperature occurs.

Ex. Combustion & Burning Mg
Energy Changes in Reactions
Endothermic Reactions

Absorb heat from the surroundings.

Surroundings will get cooler.

Need heat to keep them going.

A noticeable decrease in temperature occurs.

Ex. Photosynthesis and cold packs
Reactivity or Activity of Metals



The reactivity of a metal is based on its
ability to replace another in a compound. The
metal is oxidized.
If a single replacement reaction occurs, the
metal that “cuts in” is MORE reactive than
the one that was removed or replaced.
An activity series of metals is a listing that
ranks metals according to their reactivity.


The most active metal is at the TOP of the list
The least active metal is at the BOTTOM of the list
The ACTIVITY SERIES is listed below:
lithium
potassium
barium
strontium
calcium
sodium
magnesium
aluminum
manganese
zinc
iron
cadmium
cobalt
nickel
tin
lead
hydrogen
copper
silver
mercury
gold
The most active metal is LITHIUM
The least active metal is GOLD
Which is more active nickel or iron?
IRON
Treatment of Metals
Metals are treated to protect from
corrosion or to make the metals better
suited for specific purposes, such as,
improving strength or making them more
light weight.
 Types of Metal Treatments

Galvanizing = coating with zinc
(electroplating)
 Painting
 Making alloys = mixture of 2/more metals or
a metal and a nonmetal.

Common Alloys
 Bronze
copper + tin
 Brass
copper + zinc
 Steel
iron + carbon
Stainless steel iron, carbon + chromium
 Pewter copper, tin + antimony
 Solder lead, tin + silver
