Chemical Reaction And Equations
Made By:- Pranav Ghildiyal
Introduction to chemical reactions
• A chemical reaction is what really happens. For example, when magnesium
burns, a shiny, lustrous piece of flexible metallic ribbon is heated in the
presence of a colourless, transparent gas and changes into a white-to-grey,
opaque, crumbly, powdery solid. That is a chemical reaction.
• When water is electrolyzed, we can write that H2O becomes H2 and O2.
"H2O H2 + O2" is an equation that represents the reaction. The reaction itself
is the formation of two colourless gases, hydrogen and oxygen, when an
electric current is passed through the colourless transparent liquid, water. It is
Important that you realize the distinction between reactions and equations.
• The term "reactant" is the same as the term "reagent." It refers to each of
the chemicals that are reacting with one another; in other words, what you
have when you start the reaction. The chemicals that you get as the reaction
proceeds are called the "products." So, as a chemical reaction proceeds, you
start with reactants and you end up with products. When magnesium burns,
you have magnesium and oxygen as the reactant . The magnesium oxide is the
Introduction to chemical equations
• A chemical reaction equation is a symbolic notation system for describing chemical
changes. Reactants are the substances that are present before the chemical change.
These are written on the left side of the reaction equation. The products are the
substances that are present after the chemical change. These are written on the right
side of the reaction equation. An arrow (à) separates the reactants and the products.
An equilibrium is a chemical reaction in which the reactants are converted into
products at the same time and rate that the products are converted into reactants.
The reaction arrow for an equilibrium looks like right and left pointing arrows written
one on top of the other.
• Information about the state (solid, liquid, gas) or solution (aqueous, precipitate) is
written in parenthesis after the chemical formula.
• Coefficients are the relative number of moles of each of the reactants and
products. These numbers are written in front of the chemical formulas. In the reaction
equation below, the coefficients indicate that there are two moles of sodium
hydroxide and water for every one mole of sulfuric acid and sodium sulphate.
2NaOH(aq) + H2SO4(aq) à Na2SO4(aq) + 2H2O(l)
Parts of chemical equations
• Reactants (or 'substrates') are
two or more elements/
compounds that chemically
interact to form a new substance.
They are the starting materials for
a reaction and are always found at
the left side of a chemical
• Product(s) are formed during
chemical reactions Products have
lower energy than the reagents and
are produced during the reaction.
Products are formed as the chemical
reaction progresses toward chemical
equilibrium at a certain reaction rate,
which depends on the reagents and
Symbols Of Physical State
Balancing chemical equations
Step 1 :- Take an unbalanced equation.
Step 2 :- Draw boxes around all the chemical formulas.
Balancing chemical equations
Step 3 :- Make an element inventory.
Step 4 :- Write numbers in front of each of the boxes
until the inventory for each element is the same both
before and after the reaction.
Step 5 :- Now the equation
is balanced 7
• An exothermic reaction is a chemical reaction that is accompanied
by the release of heat. In other words, the energy needed for the
reaction to occur is less than the total energy released. As a result of
this, the extra energy is released, usually in the form of heat. Where
an exothermic reaction causes heating of the reaction vessel which is
not controlled, the rate of reaction can increase, in turn causing heat
to be evolved even more quickly . This positive feedback situation is
known as thermal runaway. An explosion can also result from the
problem. Heat production or absorption in either a physical process
or chemical reaction is measured using calorimetry. One common
Laboratory instrument is the reaction calorimeter, where the heat
flow into or from the reaction vessel is monitored. The technique can
be used to follow chemical reactions as well as physical processes
such as crystallisation and dissolution.
Examples of Exothermic reaction
• White washing
• Combustion reactions of fuels
• Neutralization reactions such as direct reaction of acid and
• Adding concentrated acid to water
• Burning of a substance
• Adding water to anhydrous copper(II) sulphate
• Reactions taking place in a self-heating can based on lime and
• The setting of cement and concrete
• Many corrosion reactions such as oxidation of metals
• Most polymerisation reactions
• The Haber-Bosch process of ammonia production
• An endothermic reaction is a chemical reaction in which energy is
absorbed from the surrounding environment in place of being released as it
is in the exothermic reaction. It is also called as a hypothermic reaction. Heat
is compulsory for this reaction as it is absorbed during the reaction takes
• melting ice cubes
• melting solid salts
• evaporating liquid water
• converting frost to water vapour (melting, boiling, and evaporation in
general are endothermic processes)
• making an anhydrous salt from a hydrate
• splitting a gas molecule
• reacting ethanoic acid with sodium carbonate
• photosynthesis (chlorophyll is used to react carbon dioxide plus water
plus energy to make glucose and oxygen)
Types of chemical reactions
• Combination Reaction
• Decomposition Reaction
• Displacement Reaction
• Double Displacement Reaction
• A combination reaction or a synthesis reaction is a general category of a chemical reaction (the term
usually refers to an inorganic chemical reaction), in which two or more reactants are chemically
bonded together to produce a single product. When two or more substances combine to form a single
product, it is known as a combination reaction. Many elements react with one another in this fashion to
• This reaction is usually exothermic because when the bond forms between the elements, heat is
released. Combination reaction has two or more reactants and one product formed by it. When a
combination reaction occurs between a metal and a non-metal the product is an ionic solid. An example
could be Lithium + Sulphur →Lithium Sulphide
A + B = C
• A combination reaction can be of three types:
a) Between two elements C + O2 → CO2
b) Between two compounds CaO + H2O → Ca(OH)2
c) Between an element and a compound O + H2O → H2O2
• A decomposition reaction is a type of chemical reaction in which a substance degrades into
two or more basic components. It is a process in direct contrast to that of chemical synthesis,
which involves molecular bonding so that two or more components may join to form a single
chemical compound. The decomposition reaction often requires exposure to a catalyst, such as
a heat source or solvent. A simple example of such a breakdown is the conversion of water
(H2O) into hydrogen (H2) and oxygen (O2) gas via a process known as the electrolysis of water.
• Decomposition chemical reactions are generally classified into three main types, which are
catalytic, electrolytic, or thermal. In catalytic reactions, an agent is introduced to cause a
chemical reaction. For example, hydrogen peroxide readily degrades into water and oxygen in
the presence of manganese dioxide. An electrolytic decomposition reaction is achieved by
exposing an aqueous solution or molten compound to an electrical current. Thermal
decomposition occurs when a compound is affected by direct heat or radiation.
C = A+ B
2HgO (s) → 2Hg (l) + O2 (g)
2Cl2O5 (g) → 2Cl2 (g) + 5O2 (g)
2N2O5 (g) → O2 (g) + 4NO2 (g)
Mg(NO3)2 (s) → Mg(NO2)2 (s) + O2 (g)
2SO3 (g) → 2SO2 (g) + O2 (g)
• Displacement reactions are the reactions in which a more
reactive element displaces a lesser reactive Element from it’s
compound is known as displacement reaction.
• These reactions are generally found to occur in solutions.
The elements involved may be metals, non-metals, i.e., a more
reactive metal may displace a lesser reactive metal or a more
reactive non-metal may displace a lesser reactive non-metal.
1. Mg + 2 H2O ---> Mg(OH)2 + H2
2. 2 KI + Cl2 ---> 2 KCl + I2
Double Displacement Reaction
• The reaction in which two compounds react by an exchange of ions to form
two new compounds .a double displacement reaction usually occurs in
solution and one of the products ,being insoluble precipitates out.
let us take an example in which we will mix the solutions of sodium chloride
and silver nitrate will precipitate out white silver chloride. nitrate ions and
chloride ions have been exchanged in this reaction.
AB + CD --> AC + BD
• Pb(NO3)2 (aq) + 2KCl(aq) -> PbCl2 (s) +2KNO3(s)
• NaCl + KBr -> NaBr + KCl
• Lead Nitrate and Potassium Iodide
• Sodium Chloride and Silver Nitrate
Oxidation and Reduction - Redox Reaction
• An oxidation-reduction reaction (redox reaction) is a reaction in
which electrons are transferred between species or in which atoms
change oxidation numbers. Oxidation is the portion of the redox
reaction in which there is a loss of electrons by a species or an increase
in the oxidation number of an atom. Reduction is the part of a reaction
in which there is a gain of electrons by a species or a decrease in the
oxidation number of an atom. Something that is oxidized loses electrons
or contains an atom that increases in oxidation number. Something that
is reduced gains electrons or has an atom that decreases in oxidation
number. An oxidizing agent is a something that oxidizes something,
meaning that the oxidation agent is itself reduced. A reducing agent is a
something that reduces something else, and is itself oxidized.
• Corrosion is the disintegration of an engineered material into its constituent atoms
due to chemical reactions with its surroundings. In the most common use of the word,
this means electrochemical oxidation of metals in reaction with an oxidant such as
oxygen. Formation of an oxide of iron due to oxidation of the iron atoms in solid solution
is a well-known example of electrochemical corrosion, commonly known as rusting. This
type of damage typically produces oxide(s) and/or salt(s) of the original metal. Corrosion
can also refer to other materials than metals, such as ceramics or polymers, although in
this context, the term degradation is more common.
• In other words, corrosion is the wearing away of metals due to a chemical
• Many structural alloys corrode merely from exposure to moisture in the air, but the
process can be strongly affected by exposure to certain substances . Corrosion can be
concentrated locally to form a pit or crack, or it can extend across a wide area more or
less uniformly corroding the surface. Because corrosion is a diffusion controlled process,
it occurs on exposed surfaces. As a result, methods to reduce the activity of the exposed
surface, such as passivation and chromate-conversion, can increase a material's
corrosion resistance. However, some corrosion mechanisms are less visible and less
• Rancidity is a very general term and in its most general meaning, it refers to
the spoilage of a food in such a way that it becomes undesirable (and usually
unsafe) for consumption. When people say that a food has "gone bad," what
they're usually talking about is rancidity. Most of the time, but not always,
rancidity can change the odours or flavours of a food in such a way that it
becomes very unpleasant to smell or taste.
• While most any food can technically become rancid, this term applies
particularly to oils. Oils can be especially susceptible to rancidity because their
chemistry can make them exceptionally susceptible to oxygen damage. When
food scientists talk about rancidity, they are often talking about a specific type
of rancidity involving oxygen damage to foods, and this type of rancidity is
called "oxidative rancidity." During the process of oxidative rancidity, oxygen
molecules interact with the structure of the oil and damage its natural
structure in a way that can change its odour, its taste, and its safety for