Balancing Chemical Equations based on the Laws of Conservation of Mass

1. CHEMICAL REACTION
Waylie Nina D. de Claro | Science 10 | Taal NHS

2. RECALL
What is a Chemical Reaction?
What is a Chemical Equation?
Give example/s of a chemical reaction
written in a chemical equation.
Identify the type of chemical reaction is
involved in the given examples.

3. Overview
• Fire has fascinated people for so long, that the ancient people
even regarded it as one of the earliest elements.
• Fire was so important to them and they described it as an
element that changes everything.
• The earliest theory about burning was the Phlogiston Theory.
• This theory by George Ernst Stahl in the 17th century stated
that when a material burns, it releases a substance known as
phlogiston, and this theory was accepted for a very long time.

4. Phlogiston (Greek phlogistos, “flammable”)
• hypothetical substance, representing flammability,
postulated in the late 17th century by the German chemists
Johann Becher and Georg Stahl to explain the
phenomenon of combustion.
• According to the phlogiston theory, every substance
capable of undergoing combustion contains phlogiston,
and the process of combustion is essentially the process of
losing phlogiston.

5. •3 factors should be present in proper
conditions and proportions.
1. Fuel
2. Oxygen
3. Heat
For burning to occur

6. • Analyze the information that can be gathered in
the chemical equation :
2 H2 + O2 → 2 H2O
• Note that the coefficient (number) placed before
the formulas indicate the number of molecules or
moles.

7. • Determiningthe correct coefficients balances
the number of atoms in the reactant and
in the product side, allowing it to follow the
•Law of Conservation of Mass.

8. Steps in Balancing Equation
• Write the unbalanced chemical equation, make sure
you have followed correctly the rules in writing
formulas of compounds.
• Take note of the elements present in the reactant and
product side.
• Count the number of atom/s of each element present
in the reactant and product side.

9. Steps in Balancing Equation
• Apply the Law of Conservation of Mass to get the
same number of atoms of every element on each side
of the equation.
• Balance chemical equations by placing the
appropriate coefficients before the symbol or formula.
• Do not change the subscripts of the formula in an
attempt to balance the equation as it will change the
identity of the components.

10. KEY CONCEPTS:
• For a chemical equation to conform to the Law
of Conservation of Mass, it has to be
balanced.
• Chemical equations are balanced by placing the
appropriate coefficients before the symbols
or formulas of reactants andproducts.
• Certain steps are observed in balancing
reactions.

11. KEY CONCEPT TO EMPHASIZE:
• Law of Conservation of Mass states that mass is
conserved in a chemical reaction. The total mass
of the reactants is equal to the total mass of the
products. No new atoms are created or
destroyed, there was only grouping or
regrouping (rearrangement) of atoms.

12. ENRICHMENT:
• Identify the type of chemical reaction and balance the following
chemical equations .
• 1. NaOH + KNO3 NaNO3 + KOH
2. CH4 + O2 CO2 + 2 H2O
3. Fe + NaBr FeBr3 + Na
4. CaSO4 + Mg(OH)2 Ca(OH)2 + MgSO4
5. NH4OH + HBr H2O + NH4Br

13. Note: Follow the Law of Conservation of mass.
Name the chemical reaction present in the following
equation. Then, balance each chemical equation.

14. Agreement/Assignment:
• Classify the following unbalanced chemical equations
according to the six types of chemical reactions and
balance if necessary.
1. P4 + O2 P2O5
2. NaNO3 NaNO2 + O2
3. C18H18 + O2 CO2 + H2O
4. H2SO4 + NaOH NaSO4 + H2O
5. 10. NiSO4 + Li3PO4 H20 + CO2