The Law of Conservation of
Mass in a Chemical Reaction
Learning Objectives
1. Apply the principle of conservation of
mass to chemical reactions (S10MTIVe-
g-23)
2. Evaluate chemical equations that
conform with the law of conservation of
mass
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Evidences of Chemical Reactions
1. Production of light
2. Evolution of Gas
3. Temperature change
4. Change in intrinsic properties (color,
odor, taste)
5. Formation of Precipitate
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How are chemical reactions
presented in a shorter way?
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Reactants Products Symbols used in Chemical
These are These are the
Equation
substances that + To show combination of
are used up to
substances reactants or products
form new produced to produce; to form; to
yield
substances in a during a heat indicates that heat is
chemical chemical supplied to the reaction
reaction reaction
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1. Iron reacts with copper (II) sulfate
and forms Iron (II) sulfate and
copper
2. Magnesium combines with oxygen
gas to produce magnesium oxide
3. Hydrogen peroxide in the
presence of manganese dioxide
produces water and oxygen gas
4. Acetic acid and sodium
bicarbonate produce sodium
acetate with the release of carbon
dioxide gas and water
5. Copper (II) sulfate reacts with
sodium hydroxide to produce
insoluble copper (II) hydroxide and
sodium sulfate solution
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A chemical equation is a chemist’s
shorthand for a chemical reaction.
It shows the symbols or formulas of
the reactants and products and the
ratio of the substances as they react.
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Law of Conservation of Mass
It 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 and
regrouping (rearrangement) of atoms.
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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
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Classification of Chemical Reactions
1. COMBINATION REACTION: Reactants combine to form a single
product.
2. DECOMPOSITION REACTION: A single reactant breaks down into
simpler ones. ( 2 or more products)
3. SINGLE DISPLACEMENT REACTION: This is when one element
replaces another element from a compound. The more active element
takes the place of the less active element in a compound.
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Classification of Chemical Reactions
4. DOUBLE DISPLACEMENT REACTION: This is when the positive ions
(cations) and negative ions (anions) of different compounds switch places
forming two entirely different compounds.
5. COMBUSTION REACTION: This is when oxygen combines with a
hydrocarbon to form water and carbon dioxide
6. ACID- BASE REACTION: This is a special type of double displacement
reaction that takes place when an acid and a base react with each other.
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Let’s have an activity!
Apply the concept of Law of Conservation of Mass in balancing chemical
equations:
1. H2 +O2 H2O
2. N2 + H2 NH3
3. CH4 +O2 CO2 + H2O
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