E.Q.: How does a balanced chemical equation support the law of conservation of matter?

1
E.Q. How does a balanced chemical equation
support the law of conservation of matter?
B Block/Period A CW N Your Name D 10-21-11
27
2

• In a chemical reaction, the amount of matter does
  not change. The atoms rearrange themselves to
  form new substances.
• The law of conservation of matter states that in
  a chemical reaction matter can not be created or
  destroyed, but can be changed in form.
• Because matter is not created or destroyed, the
  total mass of the material before the reaction is
  the same as the total mass of the material after
  the reaction.
• A balanced chemical equation has the same number
  of each kind of atom on the reactant side as on
  the product side.

3

• To determine whether a chemical equation is
  balanced, two numbers are considered the
  coefficient and the subscript.
• The coefficients are written before the chemical
  formula and indicate which particles participate
  in the reaction.
• In order to determine whether an equation is
  balanced, multiply the coefficient in front of
  the formula by the subscript written below the
  chemical symbol in the formula. If no subscript
  or coefficient is written, it is understood to be
  one.
• The number of each kind of atom on the reactant
  side must equal the number of each kind of atom
  on the product side for the equation to be
  balanced.

4

• Examples
• In the chemical equation for the reaction of
  water (liquid) breaking into hydrogen (gas) and
  oxygen (gas) as represented by the balanced
  chemical equation
• 2H2O ?2H2 O2
• There are four hydrogen atoms on the reactant
  side (coefficient of 2 x subscript 2) and four
  hydrogen atoms on the product side (coefficient 2
  x subscript 2).
• There are two oxygen atoms on the reactant side
  (coefficient 2 x (understood) subscript 1) and
  two oxygen atoms on the product side ((understood
  coefficient 1 x subscript 2).
• There are the same number of hydrogen atoms (4)
  and oxygen atoms (2) on both sides of the
  equation therefore, the equation is said to be
  balanced.
• Since there are the same number of each kind of
  atom on both sides of the arrow and atoms
  represent kinds of matter, the amount of matter
  is the same on both sides of the equation, which
  supports the law of conservation of matter.

5
How to check an equation for balance

• Draw a box around all the chemical formulas in
  the equation.
• Make an Element Inventory of the reactants and
  products.
• If the element inventory of the reactants is
  equal to that of the products, the equation is
  balanced.

6
Balanced or Not
B Block/Period A CW N Your Name D 10-24-11
27

1. H2 O2 ---gt H2O

REACTANTS PRODUCTS
Elements Coefficient X Subscript Total Number of atoms Or ? Elements Coefficient X Subscript Total Number of atoms


H
1
2
X

2
H
1
X
2

2

NOT BALANCED
2
2
O
1
1
O
1
X

X

1
?
7
B Block/Period A CW N Your Name D 10-24-11
27
Balanced or Not
2. N2 3H2 ---gt 2NH3
REACTANTS PRODUCTS
Elements Coefficient X Subscript Total Number of atoms Or ? Elements Coefficient X Subscript Total Number of atoms


N
1
2
X

2
N
2
X
1

2

BALANCED
2
6
H
2
3
H
3
X

X

6

8
B Block/Period A CW N Your Name D 10-24-11
27
Balanced or Not
3. S8 12O2 ---gt 8SO3
REACTANTS PRODUCTS
Elements Coefficient X Subscript Total Number of atoms Or ? Elements Coefficient X Subscript Total Number of atoms


BALANCED
S
1
8
X

8
S
8
X
1

8

2
24
O
8
3
O
12
X

X

24

9
B Block/Period A CW N Your Name D 10-24-11
27
Balanced or Not
4. N2 O2 ---gt
N2O
REACTANTS PRODUCTS
Elements Coefficient X Subscript Total Number of atoms Or ? Elements Coefficient X Subscript Total Number of atoms


N
1
2
X

2
N
1
X
2

2

NOT BALANCED
2
2
O
1
1
O
1
X

X

1
?
10
B Block/Period A CW N Your Name D 10-24-11
27
Balanced or Not
5. CO2 H2O ---gt
C6H12O6 O2
REACTANTS PRODUCTS
Elements Coefficient X Subscript Total Number of atoms Or ? Elements Coefficient X Subscript Total Number of atoms




1
1
1
C
X
C
1
6
6
?

X

1
12
1
2
X

H
X

12
H
2
?
NOT BALANCED
O
O
1
2
2
1
6
?
X

X
6

O
O
1
1
1

X
1
X
2
2

?
ADD the Os 213
ADD the Os 628