Chemical
Equations
and
Chemical
Reactions
Framing Questions
• What is a word equation?
• What is a skeleton equation?
• How do I balance an equation to show
that the mass of the reactants equals
the mass of the products?
Writing A Chemical
Equation
The general format for chemical
equations is:
a+ b  c +d
What Does It All Mean?
a+ b  c +d
 The reactants go on the left side of the
equation (a and b in this case).
 The + sign means “reacts with”.
 The  means “produces or yields”.
 The products go on the right side of
the equation (c and d in this case).
Lets work with the statement:
“Hydrogen gas reacts with oxygen
gas to form liquid water”
Word Equation
hydrogen + oxygen  water
Skeleton Equation
H2 + O2  H2O
To balance equations numbers
called coefficients are put before
the formulas. This changes the
number of molecules. You cannot
add or change subscripts. You do
not write coefficients of 1 (one).
Balanced Equation
___H2 + ___O2  ___H2O
2H2 + O2  2H2O
Why Must We Balance Equations?
•Remember the Law of Conservation
of Mass states that the total mass of
reactants is always equal to the total
mass of the products.
•Remember Dalton’s Atomic Theory
states that atoms can not be created
or destroyed. Compounds are formed
when atoms of different elements
combine in fixed proportions.
Sometimes you
need to
know the
state of the
chemicals
that are
involved in a
chemical
reaction.
State
solid
liquid
gas
aqueous solution
Abbreviation
State
Abbreviation
solid
(s)
liquid
gas
aqueous solution
State
Abbreviation
solid
(s)
liquid
(l)
gas
aqueous solution
State
Abbreviation
solid
(s)
liquid
(l)
gas
(g)
aqueous solution
State
Abbreviation
solid
(s)
liquid
(l)
gas
(g)
aqueous solution
(aq)
Final Balanced Chemical Equation
2H2(g) + O2(g)  2H2O(l)
Rules For Writing Balanced
Chemical Equations
This requires a lot of practice
These rules will not apply in all equations.
1. Write the skeleton equation.
2. Look for a polyatomic ion that appears once
on each side of the equation. Balance these
first.
3. Pick single elements that appear on each
side. Choose coefficients to balance this
element. The terms you balanced in the
previous step have to remain balanced.
Repeat for any other elements.
Rules For Writing Balanced
Chemical Equations, Continued…
4. Check for any term you have
not yet looked at. Adjust the
coefficient of the term so
that the numbers of the
elements appearing in that
term are balanced across the
whole equation. If you have
any fraction coefficients
clear them by multiplying.
Also, make sure you have
the smallest possible
coefficients by reducing.
5. Check the equation!
Example 1:
Word Equation
sodium + water 
sodium hydroxide + hydrogen gas
Skeletal Equation
Na + H2O  NaOH + H2
Balanced Equation
___Na + ___H2O  ___NaOH +___H2
2Na + 2H2O  2NaOH + H2
Balanced Chemical Equation
2H2O__ 2Na__ +  2NaOH__ + H2___
2Na(s) + 2H2O (l)  2NaOH(aq) + H2(g)
Verification
Reactants
2 Na atoms
Products
2 Na atoms
4 H atoms
4 H atoms
2 O atoms
2 O atoms
Example 2
Word Equation
copper + silver nitrate  copper(II)
nitrate + silver
Skeletal Equation
___ + ______  ______ + ___
Cu + AgNO3  Cu(NO3)2 + Ag
Balanced Equation
__Cu +__ AgNO3  __Cu(NO3)2 + __Ag
Cu + 2AgNO3  Cu(NO3)2 + 2Ag
Balanced Chemical Equation
Cu__ + 2AgNO3__  Cu(NO3)2__ + 2Ag__
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) +
2Ag(s)
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) +
2Ag(s)
Verification
Reactants
Products
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) +
2Ag(s)
Verification
Reactants
1 Cu atom
Products
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) +
2Ag(s)
Verification
Reactants
Products
1 Cu atom
1 Cu atom
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) +
2Ag(s)
Verification
Reactants
Products
1 Cu atom
1 Cu atom
2 Ag atoms
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) +
2Ag(s)
Verification
Reactants
Products
1 Cu atom
1 Cu atom
2 Ag atoms
2 Ag atoms
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) +
2Ag(s)
Verification
Reactants
Products
1 Cu atom
1 Cu atom
2 Ag atoms
2 Ag atoms
2 NO3- ions
Cu(s) + 2AgNO3(aq)  Cu(NO3)2(aq) +
2Ag(s)
Verification
Reactants
Products
1 Cu atom
1 Cu atom
2 Ag atoms
2 Ag atoms
2 NO3- ions
2 NO3- ions
Example 3
Word Equation
calcium nitrate + sodium hydroxide 
calcium hydroxide + sodium nitrate
Skeletal Equation
Ca(NO3)2 + NaOH  Ca(OH)2 + NaNO3
Balanced Equation
__Ca(NO3)2 + __NaOH  __Ca(OH)2 + __NaNO3
Ca(NO3)2 + 2NaOH  Ca(OH)2 + 2NaNO3
Balanced Chemical Equation
Ca(NO3)2__ + 2NaOH__  Ca(OH)2__ +
2NaNO3____
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) +
2NaNO3(aq)
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
1 Ca atom
Products
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
1 Ca atom
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
1 Ca atom
2 NO3
- ions
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
1 Ca atom
- ions
- ions
2 NO3
2 NO3
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
1 Ca atom
- ions
- ions
2 NO3
2 Na atoms
2 NO3
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
1 Ca atom
2 NO3
- ions
2 Na atoms
2
NO3 ions
2 Na atoms
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
1 Ca atom
- ions
- ions
2 NO3
2 Na atoms
2
OH
ions
2 NO3
2 Na atoms
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
Products
1 Ca atom
1 Ca atom
- ions
- ions
2 NO3
2 Na atoms
2
OH
ions
2 NO3
2 Na atoms
2
OH
ions
Homework:
P. 31
Q21 and 22