Chemical
Reactions
Reactions and Equation
Chemical reaction is the process in which atoms of one or more substances are
rearranged to from a different substance.
Chemical reaction is another name of chemical change.
Chemical reactions can be represented by balanced chemical equations.
Evidence of chemical reaction
 Temperature change, heat of light releases or absorbed.
 Solid formation, precipitation.
 Gas formation, bubbles.
 Odor
 Color change
Chemical equation
 Chemical equation represents chemical reactions.
 Reaction reactants, starting substance, in left side of the arrow.
 Reaction products, substances that are formed during reaction, right side of the arrow
 Arrow, used to separate reactants from products, read as react to produce or yields.
 Plus, sign, used to separate two reactants or two products.
 Another arrow is used that indicates a reversible reaction.
 Physical state gives a clue of how a reaction occur.
Solid state (s)
Liquid state (l)
Gaseous state (g)
Water solution state (aq) = dissolved in water = aqueous solution
Ways to represent chemical equations
 Word Equation:
uses statements and words to represent reactants and products.
Lack for important information’s.
 Skeleton equation:
An equation that uses chemical formulas unlike word
equation.
Lack for important information’s such as to show that matter
cannot me created nor destroyed.
 Balanced chemical Equation:
A statement that uses chemical formulas to show identities,
and relative amount of the substances involved in reaction.
Uses coefficients to balance the equation.
Coefficient: is number used to balance a chemical equation, written in
front of the reactants or product. Usually written as whole number, and if
it is one it will not be written,
It described the lowest whole possible ratio of the number of reactants
and products.
Classifying Chemical Reactions
¥ Classifying chemical reactions helps to understand, remember and to
organize different chemical reactions.
¥ Also helps to recognize a pattern and to predict the product of
reactions.
¥ Four different types of chemical reactions are synthesis, combustion,
decomposition, and replacement reaction.
¥ Some reactions can fit into more than one type.
Synthesis Reaction
A synthesis reaction is a chemical reaction in which two
or more substances react to produce single product.
A+B
AB
Element with element: Sodium react with chlorine to
produce sodium chloride.
Compound with compound: Calcium oxide react with
water to produce calcium hydroxide.
Compound with element: Sulfur dioxide gas react with
oxygen gas to produce sulfur trioxide.
Combustion Reaction
Combustion reaction is a chemical reaction in which oxygen reacts with
a substance and releases energy in form of heat and light.
A+ 𝑶𝟐
AO
Example: Reaction between hydrogen and oxygen when hydrogen is heated
and produce water, where a large amount of energy is released.
Example2 : When Coal is burned, since it contain carbon and it react
with oxygen this equation shows what happens: C+𝑶𝟐
C𝑶𝟐
Hydrocarbons:
A group of substances that all contain hyrdrogen and carbon, and burns oxygen
to produce carbon dioxide and water.
For example: Methane CH4
Decomposition Reaction
The opposite of synthesis reaction is decomposition reaction.
Decomposition reaction is a chemical reaction in which a single compound
breaks down into two or more elements or new compounds.
AB
A+B
For decomposition reaction to start energy source is required such as heat,
light and electricity.
Example: Automobile saftey air bag when it inflate rapidly as sodium azide
decompose.
 It decompose as the electric signal in package in the air bag warn. As soon
as it warn sodium azide breaks down into nitrogen gas and the air bag inflate
quickly.
Replacement Reaction
Replacement Reaction is a chemical reaction that involves the replacement of
elements in a compound.
It’s also called displacement reaction.
Two types: Single replacement reaction and double replacement reaction.
Single replacement Reaction
Single replacement reaction is a reaction in which atom of an
element replaces the atom of another element.
A+BX
AX+ B
Hydrogen Replacement: Metal with Hydrogen
A metal should replace another metal in a compound dissolved in
water that is less reactivity than it.
Nonmetal replacement: Halogen’s replacement – most
reactive fluorine and least Iodine.
Also, nonmetal should replace another nonmetal less than it
in reactivity.
Double replacement reaction
Double replacement reaction involves exchanging of
ions between two compounds.
AX+ BY
AY+BX
Anions switch places, Y replaces X and X replaces Y.
Positive ions and negative ions switch places.
All double replacement reactions produce either
water, precipitation, or gas.
STEP 1
Write skeleton equation for the
reactants.
STEP 2
Identify the anions and cations.
STEP 3
Pair the cations with anions of
STEP 4
Write the equation with the pairs in
STEP 5
Write the complete chemical equation.
STEP 6
Balance the equation.
different compounds.
step3.
Precipitation = a solid produced during chemical