Chemical
Equations
and
Chemical
Reactions
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.
• 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)
Step 1:
•
•
Write in the symbols for all atoms and ions
(skeleton equation)
Balance each compound
–
–
Remember diatomic ions: H2, N2, O2, F2, Cl2, Br2, I2
Remember to look for polyatomic ions on both sides of
the equation
iron + water  hydrogen gas + iron (III)
oxide
Fe + H2O  H2 + Fe2O3
Step 2:
• Write in the abbreviations for the state of each
compound if known or given
Solid = (s)
Liquid = (l)
Gas = (g)
Aqueous solution = (aq)
ex. Fe (s)
ex. H2O (l)
ex. He (g)
ex. NaCl (aq)
• Fe (s) + H2O (l)  H2 (g) + Fe2O3 (s)
Step 3: Balance Equation
• Balance the equation by adding coefficients
– Pick single elements that appear on each side first to
balance
– Remember leave O then H until the end
• Go back and re-check that all atoms are equal on both
sides
– If you have any fraction coefficients clear them by
multiplying.
– Also, make sure you have the smallest possible
coefficients by reducing the ENTIRE EQUATION.
2Fe (s) + 3H2O (l)  3H2 (g) + Fe2O3 (s)
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 Products
1 Cu atom
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)
Reacta Produc
nts
ts
1 Ca
atom
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactan Products
ts
1 Ca
1 Ca
atom
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
2 NO3- ions 2 NO3- ions
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants Products
1 Ca atom 1 Ca atom
2 NO3 ions 2 NO3 ions
2 Na atoms
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
1 Ca atom
2 NO3 ions
2 Na atoms
Products
1 Ca atom
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
2 NO3- ions 2 NO3- ions
2 Na atoms 2 Na atoms
2 OH- ions
Ca(NO3)2(aq) + 2NaOH(aq)  Ca(OH)2(s) + 2NaNO3(aq)
Reactants
1 Ca atom
2 NO3 ions
2 Na atoms
2 OH ions
Products
1 Ca atom
2 NO3 ions
2 Na atoms
2 OH ions
Homework:
P. 174 # 1 to 4