Unit 6:
Chemical Equations &
Reactions Part 1
Independence HS: Chemistry
Chapter 10
Section 10.1 Reactions and Equations
• Recognize evidence of
chemical change.
• Represent chemical
reactions with equations.
• Balance chemical
equations.
Chemical reactions are
represented by balanced
chemical equations.
chemical change: a
process involving one or
more substances changing
into a new substance
chemical reaction
reactant
product
chemical equation
coefficient
NGSS Standard: HS-PS1-7: Use mathematical representations to support the claim that
atoms, and therefore mass, are conserved during a chemical reaction.
Chemical Reactions
➢The process by which
one or more substances
are rearranged to form
different substances is
called a chemical
reaction
➢Evidence?
➢–Change in
temperature
➢–Change in color
➢–Odor, gas, or
bubbles may form.
• Chemical Equation- A chemical equation is a
written representation of the process that occurs
during a chemical reaction.
• Chemical Equation & Reaction Symbols: a short,
easy way to show chemical reactions
plus signs separate two or more
reactants and also two or more products
4 Fe + 3O2
2Fe2O3
horizontal arrow means the reaction
yields or produces something
• Chemical Formulas and Names:
letters and numbers that represent a
molecule
Formula: Fe2O3
Name: Iron Oxide
• Reactants: the substances in a
chemical reaction that change into
new substances. They are on the left
side of the equation.
4 Fe + 3O2
reactants
2Fe2O3
• Products: the substances that are
formed in a chemical reaction. They
are on the right side of the equation.
4 Fe + 3O2
2Fe2O3
product
• Subscripts: small numbers to the right of
the element symbols that give the number
of atoms
4 Fe + 3O2
2Fe2O3
• Coefficient: large numbers in front of the
element symbols that give the number of
molecules
4 Fe + 3O2
2Fe2O3
Chemical Equations
reactants
products
SnO2(s) + 2H2(g) → Sn(s) + 2H2O(g)
subscript
state of
matter
coefficient
yield sign
Chemical Equations
❖ We can express a reaction using words
❖ We can express a reaction using chemical
equations
Reactants (LEFT)
substances that
undergo a reaction
Products (RIGHT)
new substances
formed in a reaction
Law of Conservation of Mass
• You should know THIS, too!
• In a chemical reaction, matter is neither
created nor destroyed
• In other words, the number and type of
atoms going INTO a reaction MUST be
the same as the number and type of
atoms coming OUT
• If an equation obeys the Law of
Conservation, it is balanced.
An Unbalanced Equation
• CH4 + O2 🡪 CO2 + H2O
Reactant Side
Product Side
1 carbon atom
2 hydrogen atoms
3 oxygen atoms
1 carbon atom
4 hydrogen atoms
2 oxygen atoms
NOT THE SAME!
A Balanced Equation
●
CH4 + 2O2 🡪 CO2 + 2H2O
Reactant Side
Product Side
1 carbon atom
4 hydrogen atoms
4 oxygen atoms
1 carbon atom
4 hydrogen atoms
4 oxygen atoms
BOTH ARE EQUAL!
Rules of the Game
1. Matter cannot be created or destroyed.
2. Subscripts CANNOT be added, removed, or
changed.
3. You can ONLY CHANGE coefficients.
4. Coefficients can only go in front of chemical
formulas...NEVER in the middle of a formula.
A few extra tips:
⚫Try balancing big formulas first; save the free elements
for last
⚫If the same polyatomic ion appears on both sides of the
equation, it’s okay to treat it as one unit
⚫There is no one particular way to balance equations. Some
equations are harder to balance than others and might
require some creativity to solve
Balancing Equations
⚫Balance the following equation by adjusting
coefficients 🡪 Make a “t” chart to help!
N2 + 3 H2 🡪 2NH3
reactants products
N
2
21
H
6
2
63
Balancing Equations
• Balance the following equation by adjusting
coefficients 🡪 Try the “t” chart again!
2 KClO3 🡪 2KCl + 3 O2
reactants products
K
1
2
12
Cl
1
2
1
2
O
3
6
2
6
Balancing Equations
• Balance the following equation by adjusting
coefficients 🡪 Try the “t” chart again! 🡪 THIS IS
TOUGH!
Fe2O3 + 3 H2SO4 🡪 Fe2(SO4)3 + 3 H2O
reactants products
Fe
2
2
O
3
3
1
H
6
2
62
SO4 3
1
3
Remember!
Balance the larger
molecules first…
leave the single
atoms until last!
Balancing Chemical Equations
Practice
➢ Write a balanced chemical equation for the following
reactions.
A) ___ K(s) + ___ H2O(l) → ___ H2(g) + ___ KOH(aq)
B) ___ CaCl2(aq) + ___ Na2CO3(aq) → ___ CaCO3(s) + ___ NaCl(aq)
C) ___ N2(g) + ___ H2(g) → ___ NH3(g)
Balancing Chemical Equations
Practice
➢ Write a balanced chemical equation for the following
reactions.
2 K(s) + ___ H22O(l) → ___ H2(g) +
1 ___ KOH(aq)
A) ___
2
1 CaCl2(aq) + ___ Na2CO
1 3(aq) → ___ CaCO3(s) + ___
1 NaCl(aq)
B) ___
2
1 N2(g) + ___ H32(g) → ___ NH3(g) 2
C) ___
Word Equations
Translate the following word equation into an
chemical equation:
Hydrogen chloride in the liquid phase and
sodium hydroxide in the solid phase yields
aqueous sodium chloride and water
Word Equations
Hydrogen chloride in the liquid phase and
sodium hydroxide in the solid phase yields
aqueous sodium chloride and water
HCl (l) + NaOH (s)
NaCl (aq) + H20
Part 2: Classifying and
Predicting Reactions
Synthesis Reaction
➢Whenever two or more
substances combine to
form a single product,
the reaction is called a
synthesis reaction.
Decomposition Reaction
➢Whenever a compound
breaks down into two or
more simpler substances,
the reaction is called a
decomposition reaction.
2H2O2(aq) → 2H2O(l) + O2(g)
Single-Replacement Reaction
➢Whenever one element
takes the place of
another, the reaction is
called a singledisplacement reaction.
Activity Series
Li
Rb
K
Ca
Na
Mg
Al
Mn
Zn
Fe
Ni
Sn
Pb
H2
Cu
Hg
Ag
Pt
Au
Most Active
• This feature is found on your handy helper.
• Use it to determine whether a singledisplacement reaction will occur (react) or not.
Least Active
Activity Series
Li
Rb
K
Ca
Na
Mg
Al
Mn
Zn
Fe
Ni
Sn
Pb
H2
Cu
Hg
Ag
Pt
Au
Most Active
Example #1: Is this combination possible?
Pb + MgSO4 → PbSO4 + Mg
Answer: No, because Mg is more active than Pb
Example #2: Is this combination possible?
NaNO3 + K → Na + KNO3
Answer: Yes, because K is more active than Na
Least Active
Double-Replacement Reaction
➢Whenever two ionic compounds
trade cations, the reaction is
called a double-displacement
reaction.
➢One of the products will
either be water, a gas, or
most commonly a precipitate
(insoluble in water).
Combustion Reaction
➢ Whenever hydrocarbons
combine rapidly with oxygen
(usually by fire), the reaction is
called a combustion reaction.
Classifying Chemical Reactions
➢Reactions are classified into several categories.
➢ Synthesis (direct combination)
➢ Decomposition
➢ Single Replacement
➢ Double Replacement
➢ Combustion
A + B → AB
AB → A + B
A + BC → AC + B
AB + CD → AD + CB
CxHy + O2 → CO2+ H2O
• By recognizing these patterns, you can
classify a reaction and make predictions
about its products.
• Compare these reactions to dancing!
Identifying Chemical Reactions
➢ Identify each of the following chemical equations as
synthesis, decomposition, single-displacement, doubledisplacement, or combustion reaction.
A)
B)
C)
Predicting Chemical Reactions
Steps
1. Determine what type of reaction is being presented
2. Write the correct formulas for the product(s)
3. Balance the equation
Example: CaCl2 + Al(OH)3 → ?
1. Double-displacement reaction
2. __CaCl2 + __Al(OH)3 → __Ca(OH)2 + __AlCl3
3. 3CaCl2 + 2Al(OH)3 → 3Ca(OH)2 + 2AlCl3
Predicting Chemical Reactions
Practice
➢Predict the chemical reaction from combining
sodium iodide with strontium hydroxide:
2NaI(aq) + Sr(OH)2(aq) → 2NaOH(aq) + SrI2(s)
➢Predict the chemical reaction from combining
magnesium and copper (II) sulfate:
Mg(s) + CuSO4(aq) → Cu(s) + MgSO4(aq)