Download Chemical Equations and Reactions - ahs

Chemical Equations and
Reactions
You should be able to
- classify reactions by type
- write a balanced molecular equation
Chemical reactions
Chemical
equations
- balancing equations
- law of conservation
of mass
Chemical
equations
-
synthesis
decomposition
single replacement
double replacement
combustion
Signs of Chemical Reactions
There are five main signs that indicate a chemical reaction has taken place:
release
input
change in color
change in odor
production of new
gases or vapor
https://www.youtube.com/watch?v=JSiBSSFKRwE
input or release
of energy
difficult to reverse
Illinois State University, Jeff Christopherson; 2002
Chemical Equations
aluminum oxide
Depict the kind of reactants and products and their relative
amounts in a reaction.
4 Al(s) + 3 O2(g)
reactant
2 Al2O3(s)
product
The letters (s), (g), and (l) are the physical states of compounds.
The numbers in the front are called stoichiometric coefficients.
Chemical Equations
4 Al(s) + 3 O2(g)
2 Al2O3(s)
4 g Al + 3 g O2 yield 2 g Al2O3
This equation means:
4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3
or
4 Al moles + 3 O2 moles yield 2 moles of Al2O3
Chemical Equations
Because the same atoms are present in a reaction at the
beginning (reactants)and at the end (products), the amount
of mass in a system does not change.
The Law of Conservation of Mass
100%
Kotz web
Chemical
Factory
100%
Chemical Equations
Because of the principle of the conservation of mass,
An equation must be balanced.
It must have the same number of atoms
of the same kind on both sides.
Lavoisier, 1788
Chemical Equations
methane
+
oxygen
carbon dioxide
Reactant
CH4 +
2 O2
+
water
Product
CO2
+
2 H2O
Unbalanced and Balanced Equations
H
Cl
Cl
H
H
H
H
Cl
H2 + Cl2 → HCl (unbalanced)
reactants
H
Cl
2
2
H
H
Cl
Cl
Cl
H2 + Cl2 → 2 HCl (balanced)
reactants
products
1
1
Cl
H
Cl
2
2
products
2
2
Steps for Balancing Chemical Equations
1. Write skeleton equation
2. Count the atoms of each element in the reactants.
*Remember polyatomic ions
3. Count the atoms of each element in the products.
4. Add coefficients so that you have the same number of
atoms of each element on both sides.
5. Write coefficients in their lowest possible ratio.
General Chemical Equation
● Use letters of the alphabet (A,B,C,D) in place of chemical symbols for
elements to provide basic structure for each type of reaction
Ex: A + B → AB
instead of: H2 + O2 → H2O (skeleton equation)
Activity: General Equation Dance
Task:
1. In groups, read the section of
the textbook related to your
group’s assigned chemical
reaction.
2. Come up with a short
dance/representation of that
type of reaction based on their
general chemical equation.
3. Present to your peers.
Types of chemical
equations
1. Synthesis
2. Decomposition
3. Single
displacement
4. Double
displacement
5. Combustion
Inspirational Video
1.Synthesis
● A + B → AB
● Two elements combine to form a compound
● Can be:
○ metal + non-metal
○ non-metal + non-metal
ex: H2 + O2 → 2H2O
2H2 + 2O2 → 2H2O
2. Decomposition
● AB → A + B
● A compound is broken apart into two or more
elements or simpler compounds.
● Products can be:
○ metal + nonmetal
○ non-metal + non-metal
● Opposite of synthesis
● ex: H2O → H2 + O2
2H2O → 2H2 + O2
3. Combustion
Chemical or compound reacts quickly with oxygen gas
usually a hydrocarbon
give off heat and light
CxHy + O2 → H2O
ex:
+ O2 →
CO+2 +
O
CHCH
CO
2HH22O
4 + 42O2 →
2
4. Single Displacement
AB +C → CB + A
Element reacts with ionic compound
Element kicks out part of the ionic compound
The elements that switch places must be either two metals or
two non-metals
3CuCl
→ AlCl
AlCl22 ++ CU
3Cu
ex:
CuCl2 2++2Al
Al →
5. Double Displacement
AB + CD → AD + CB
The positive or negative ions in two dissolved ionic
compounds switch places
ex: Mg(OH)2 + AgNO3 → Mg(NO3)2 + AgOH
Mg(OH)2 + 2AgNO3 → Mg(NO3)2 + 2AgOH
Additional Resources for Review
Khan Academy- Balancing Chemical Equations
https://goo.gl/3eje5L