by Maryam Hussain
What is a chemical equation?
A chemical equation is
merely a representation of a chemical reaction in the chemist's shorthand.
A chemical reaction is what
happens when one substance meets and reacts with another and a new substance is
formed. The substances that react together are called reactants, and
those formed are called products.
The chemical properties of
reactants involved in a chemical reaction are different from those of products. Chemical
properties are characteristics that involve chemical change. A
chemical property of hydrogen gas is that it combines with oxygen gas to
form water (liquid). A chemical property of chlorine gas is that it
combines with sodium metal to form table salt, a non-metal solid. A chemical
property of gasoline is that it ignites to undergo combusts to produce carbon
dioxide and carbon monoxide and a lot of heat.
A chemical equation obeys the
“law of conservation of mass” which states that mass is neither created nor
destroyed. This applies to the mass of the atoms involved in a reaction and can
be shown in a chemical equation.
In a chemical equation, the
symbols and formulas of the substances present before the reaction takes
place are written to the left and separated by a plus (+) sign. An arrow
pointing to the right signifies a chemical change. Symbols and formulas of the
elements or compounds that form as a result of the reaction appear on the
right.
What are components of a
chemical equation?
A chemical equation is
composed of the following three fundamental parts:
1. Reactants(s)
2. A-line,
with an arrowhead, from reactant(s) to product(s), called a reaction arrow,
3. Product(s)
A chemical equation consists of
the following very frequently used components:
1. A
sign of addition that is +
2. Conditions
of reaction e.g.
A. heat,
B. aq,
where aq means an aqueous solution
C. Temperature
value or range of temperature
D. Pressure
value or range of pressure
E. Name,
symbol, or formula of catalyst used
Where the conditions of a
chemical reaction are written in a chemical equation?
Conditions of reaction e.g. temperature,
catalysts, etc. are often placed above or under the reaction arrow. The use of
the term with brackets (aq) refers to an aqueous solution; this is not a state
of matter.
300 oC, 100 bar
Reactant-A + Reactant-B ⇀ Products
aq,
Pt or Pd
Where, 300 oC,
100 bar, aq, Pt, or Pd are temperature, pressure, aqueous, and catalyst
specifications or conditions for the given reaction.
What abbreviations are used
for physical states of reactants and products in a chemical reaction?
In chemical equations, the states
of a substance are often included and the standard abbreviations are:
solid (s)
liquid (l)
gas (g)
What is a catalyst?
A catalyst can be an element or
mixture of different elements, OR a compound or mixture of different compounds
that participates in a particular chemical reaction and thereby increases the
rate of that chemical reaction, but without a net change in the amount/mass of
that catalyst in the system. Catalysts can be gases, liquids, or solids.
The catalysts used for the production of sulphuric acid through the contact
process are Pt, V2O5; where Pt is a
platinum element while V2O5 is a
compound.
What is a Substance?
A substance is a pure form of a chemical compound that has a unique set of properties by which this matter can be recognized and it cannot be separated into two or more different species by any physical technique at ordinary temperatures. For example, if water boils at a specific temperature, or freezes at a specific temperature, w.r.t prevailing ambient pressure, then it is a substance; further, it cannot be broken down into its hydrogen and oxygen contents by physical means.
What is a chemical form of a
substance?
In a chemical equation, any one
or more of the reactant(s) and any one product or more of the product(s) may be
in the same or different chemical forms e.g. molecules, ions & radicals. In
a given chemical equation, the chemical form of a (specie) ion, molecule
compound, ionic compound, or radical is not explicitly mentioned. We shall
briefly explain each of these terms.
What is a chemical formula?
The chemical formula of a
substance is an alphanumeric notation that uses atomic symbols with numerical
subscripts to represent the relative proportions of atoms of the different
elements in the substance.
For example, the chemical formula of water is
H2O; it shows that the compound is composed of hydrogen and
oxygen elements in 2:1 respectively. Also, the chemical formula of sodium
chloride is NaCl.
When no subscript is shown for
a symbol in a chemical formula then its means that all elements in the
given formula are in proportion of 1. There are two types of chemical formula,
from merely a naming point of view; one is called molecular formula and the other
is called formula unit or chemical formula of an ionic compound.
What is an ion?
Atoms are capable of gaining or
losing electrons. When an atom gains or losses electron(s) then an
electrostatic charge is automatically developed on this atom and, now, this
atom is called an ion.
Ions are electrically charged
atoms because they have an imbalance of protons and electrons, while
protons and electrons are positively and negatively charged subatomic
particles.
It is possible for a single atom
to be charged. It is also possible for a group of atoms to collectively develop
a single charge. There are two types of ions w.r.t type of charge. Ions that
possess a positive charge, such as the sodium ion, Na+, are
called cations. Ions that possess a negative charge, such as
the chloride ion, Cl-, are called anions.
What is a molecule &
molecular compound?
A molecule is a group or a
cluster of atoms held together by means of chemical bonding. A molecule is the
smallest cluster of an element or a compound that can have a stable independent
existence. There are two types of molecules on the basis of (i) the same &
(ii) different elements in a molecule.
Molecules of an Element:
When at least two single atoms of
the same element combine together by means of a chemical bond then a diatomic
(composed of two atoms) molecule of an element is formed. For example, the
oxygen gas that we inhale is a diatomic molecule having a molecular formula of
O2.
Molecules of a Compound:
When at least two atoms of
different elements are held together by means of a chemical bond then a
diatomic (composed of two atoms) molecule of two different elements is formed.
For example, a molecule of hydrogen chloride (HCl).
Similarly, when three atoms of
different elements are held together by means of a chemical bond then a
tri-atomic (composed of three atoms) molecule of three different elements is
formed. For example, a molecule of water (H2O).
Molecular formula:
A molecular formula gives
the exact number of different atoms of an element in a molecule. For example,
the hydrogen peroxide molecule contains two hydrogen atoms and two oxygen atoms
chemically bonded. Therefore, its molecular formula is H2O2.
A molecular formula is used to represent a molecular compound in a chemical
equation and other literature.
How to define the chemical
formula of an ionic compound?
A formula unit is the smallest
possible integer number of different ions in an ionic compound. A formula unit
is used to represent an ionic compound in a chemical equation and other
literature. For example, sodium chloride is an ionic compound and NaCl is its
formula unit.
What is a radical?
A radical, or free radical, is a chemical species containing one or more unpaired electrons. For example, sulfate radical SO4- -, ammonium radical NH4+. A radical is often used in the sequence of chemical equations representing the reaction mechanism.
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