The document discusses chemical reactions, including defining a chemical reaction as the rearrangement of atoms to form new substances. It identifies indicators that a reaction occurred and explains that reactions are represented by balanced chemical equations. The document provides steps for balancing equations, including identifying elements and applying the law of conservation of mass. It also gives examples of balanced and unbalanced equations and an activity to practice balancing equations.

1. CHEMICAL
REACTIONS
Week 5

6. OBJECTIVES:
• Apply the principles of conservation of mass to chemical reactions.
• Specifically:
• Explain chemical reactions
• Identify and describe the types of chemical reactions
• Balance the chemical equations

7. • A chemical reaction refers to a process in which atoms of the same different elements
rearrange themselves to form a new substance.
• There are several indicators that a chemical reaction has taken place such as: gas bubbles
appear; formation of precipitate; color change; temperature change; production of
light; volume change and change in smell or taste.
• Chemical reactions can be represented by chemical equations. The equation distinguishes
between the reactants, which are the starting materials and the products which are resulting
substance/s.
• It shows the symbols or formulas of the reactants and products, the phases (gas, solid,
liquid) of these substances, and the ratio of the substances as they react. Example: Zn
+ S → ZnS (Zinc + Sulfur → Zinc Sulfide)
• In this example, the reacting substances (reactants) are shown on the left of the arrow or the
Zn + S and the resulting substances from the reaction are written on the other side of the
arrow or the ZnS.

9. • Steps in Balancing Equations
• 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.
• 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. • Example:
• Zn + HCl → ZnCl2 + H2
•
Rea ctant Product
No. of atom/s Element No. of
atom/s
Element
1 Zn 1 Zn
1 H 2 H
1 Cl 2 Cl

11. Zn + 2HCl → ZnCl2 + H2
Reactant Product
No. of
atom/s
Element No. of atom/s Element
1 Zn 1 Zn
2 H 2 H
2 Cl 2 Cl

12. Chemical Reaction Reactant/s Products/
s
CH4+ 2O2 → CO2 + 2H2O
CaO+CO2 → CaCO3
Pb+FeSO4 → Pb SO4 + Fe
H2SO4 + NaOH →NaSO4 +
H2O
BaS + PtF2 → BaF2 + PtS

13. • Direction: Classify the following unbalanced chemical equations according to the six types of
chemical reactions.
• NaOH + KNO3 → NaNO3 + KOH
• CH4 + O2 → CO2 + 2 H2O
• Fe + NaBr → FeBr3 + Na
• CaSO4 + Mg(OH)2 → Ca(OH)2 + MgSO4
• NH4OH + HBr → H2O + NH4Br
• P4 + O2 → P2O5
• NaNO3 →NaNO2 + O2
• C18H18 + O2 → CO2 + H2O
• H2SO4 + NaOH →NaSO4 + H2O
• NiSO4 + Li3PO4 → Ni3(PO4)2 + Li2SO4

14. • Activity 3: Balance Act
• (Adapted from DepEd Science 10 Learner’s Material page 421)
• Direction: Balance the following chemical equations, make sure to apply the principle
of the Law of Conservation of Mass.
• Fe2O3 + C → Fe + CO2
• CH4 + O2 → CO2 + H2O
• Fe + NaBr → FeBr3 + Na
• SiCl4 + H2O → SiO2 + HCl
• N2 + O2 + H2O → HNO3
• P4 + O2 → P2O5