Law of Conservation of Mass/Matter states that the mass of the sum of the reactants will always equal the mass of the sum of the products. Thus, it also indicates that matter (atoms) are neither created or destroyed in a chemical reaction; they are conserved. This is the reason why we balance chemical equations.
Balancing Chemical Equations: It is trial and error approach but here are some rules to help…
1.
Make sure the formulas are correct for all the products and reactants (correct symbols and subscripts).
2.
Count the number of atoms of each element on both sides of the equation. A polyatomic ion (such as SO
4
-2 ) that is unchanged on both sides of the equation counts as a single unit, as if it were an element.
3.
Balance the elements one at a time using coefficients (a big number in front of the chemical formulas). Subscript numbers can NOT be changed. You may use an atomic inventory table to help.
4.
Make sure all the coefficients are in the lowest whole number ratio.
Skeleton Equation (not balanced) Balanced Equation (equal atoms on both sides)
___ N
2
(g) + ___ H
2
(g)

___ NH
3
(g) AFTER N
2
(g) + 3 H
2
(g)

2 NH
3
(g)
N 2
H 2
|
|
1
3
N 2
H 6
|
|
2
6
A Skeleton Equation (not balanced) is shown below with an atomic inventory taken…fix the inventory using coefficients and balance this equation. Notice how nitrate and sulfate are counted as single units.
___ Sn(NO
3
)
4
(aq) + ___ CaSO
4
(aq)

___ Sn(SO
4
)
2
(aq) + ___ Ca(NO
3
)
2
(aq)
Sn 1 | 1
NO
3
4
Ca
SO
4
1
1
|
|
| 2
2
1

Law of Conservation of Mass/Matter states that the mass of the sum of the reactants will always equal the mass of the sum of the products. Thus, it also indicates that matter (atoms) are neither created or destroyed in a chemical reaction; they are conserved.
This is the reason why we balance chemical equations.
Balancing Chemical Equations: It is trial and error approach but here are some rules to help…
1.
Make sure the formulas are correct for all the products and reactants (correct symbols and subscripts).
2.
Count the number of atoms of each element on both sides of the equation. A polyatomic ion (such as SO
4
-2 ) that is unchanged on both sides of the equation counts as a single unit, as if it were an element.
3.
Balance the elements one at a time using coefficients (a big number in front of the chemical formulas). Subscript numbers can NOT be changed. You may use an atomic inventory table to help.
4.
Make sure all the coefficients are in the lowest whole number ratio.
Skeleton Equation Balanced Equation
(not balanced) (equal atoms on both sides)
__N
2
+ __ H
2

__ NH
3
N
2
(g) + 3 H
2
(g)

2 NH
3
(g)
N 2 | 1 N 2 | 2
H 2 | 3 H 6 | 6

A Skeleton Equation (not balanced) is shown below with an atomic inventory taken…fix the inventory using coefficients and balance this equation. Notice how nitrate and sulfate are counted as single units.
__ Sn(NO
3
)
4
+ __ CaSO
4

__ Sn(SO
4
)
2
+ __ Ca(NO
3
)
2
Sn 1 | 1
NO
3
4 | 2
Ca 1 | 1
SO
4
1 | 2