Chemical Reaction
When two or more substances are brought
into contact with each other and they produce new substance(s). This
process is called chemical reaction or chemical change.
When we put chemical solutions
together there is always the possibility that there will be a chemical reaction
and it is also equally possible that there will be no chemical reaction.
The substances that initially
involved in the chemical reaction are called reactants or reagents. The
reactants transform into one or more products, which usually have properties
different chemical properties as that of reactants.
Chemical reactions
involve breaking chemical bonds of reactant molecules and forming new
bonds in product molecules by the rearrangement of atoms. The number of atoms
before and after the chemical reaction is the same but the number of molecules
will change.
During the chemical reaction, following change we observe:
- Evolution of gas.
- Formation of a precipitate.
- Change in color.
- Change in temperature.
- Change in state.
- Formation of new substances.
Representation
of chemical reaction:
A chemical equation is a symbolic representation of a chemical reaction in which the reactants and products are denoted by their respective chemical formulae.
Chemical reaction between carbon and oxygen gas form carbon dioxide gas.
Word equation:
Carbon + Oxygen gas → Carbon dioxide
Chemical Equation:
C + O2 → CO2
Balancing of Chemical equations:
Balancing of a Chemical equation is based on the concept of atom conservation i.e. conservation of mass, which states that the total number of atoms of each element in reactants must equal the number of atoms of element in products. It is a derivation of law of Mass.
- Count each atoms in reactants and products. Does atoms appear on both sides of the arrow have same counting? If not, the equation is not balanced, and you have to go to next step.
- Start balancing of atom from molecule containing maximum number of atoms in chemical reactions.
- Put coefficients in front of the symbols or formulas of molecules to increase the number of atoms of the substances. Use the smallest coefficients possible.
- Repeat steps 3 until the equation is balanced.
Balance this chemical equation for the reaction in which nitrogen (N2) and hydrogen (H2) combine to form ammonia (NH3):
N2 + H2 → NH3
1. Identify molecule containing maximum number of atoms in chemical reaction. Here it is NH3 containing 4 atoms.
2. Proceed for balancing either H atom or N atom. Here we balance N first.
3. Put co-efficient 2 before NH3 molecule to balance N atom.
N2 + H2 →2 NH3
4. Put co-efficient 3 before H2 molecule to balance H atom.
N2 + H2 →2 NH3
Thus, Chemical equation is balanced.
Different Types of Chemical Reactions
Chemical reactions are:
1. Combination reaction
2. Decomposition reaction
3. Displacement reaction
4. Double Displacement reaction
5. Precipitation Reaction
6. Oxidation and Reduction
Combination Reaction
A chemical reaction in which two or more reactants combine together and form a single product is known as a combination reaction. X + Y → XY
It is also known as a synthesis reaction.
Example:
2Na + Cl2 → 2NaCl
2H2 + O2 → 2H2O
Exothermic Reaction
Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.
Burning of natural gas:
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g)+Heat
Endothermic Reaction
Reactions in which the reactants absorb heat energy from the surroundings to form products is called endothermic chemical reaction.
Dissolving of Ammonium nitrate in water:
NH4NO3(s) + H2O(l) + Heat→ NH4NO3(aq)
Photosynthesis:
6 CO2(g) + 6 H2O(l) + light energy → C6H12O6(aq) + 6 O2(g)
Decomposition Reaction
A chemical reaction in which a single
compound breaks into two or more molecules or compounds is known as a
decomposition reaction.
XY → X + Y
It is opposite of a combination reaction.
CaCO3(s) + Heat → CaO(s) + CO2(g)
2FeSO4(s) + Heat → Fe2O3(s) + SO2(g) + SO3(g)
Displacement Reaction
A chemical reaction in which a more reactive element displaces a less reactive element from its aqueous salt solution.X + MN → XN+ M
(X is more reactive than M so N is displaced from MN by X)
It is also known as substitution reaction
Example: Zn + CuSO4 → ZnSO4 + Cu
Double Displacement Reaction
A chemical reaction in which ions get exchanged between two reactants which form a new compound is known as double displacement reaction.XY + MN → XN + YM
It is also called a metathesis reaction.
BaCl2 + Na2SO4 → BaSO4 + 2NaCl
Precipitation Reaction
The reactants are soluble,
while the products formed are insoluble and separates out as a precipitate or
solid.
Oxidation and Reduction
Oxidation is defined as “adding oxygen,” or “removing of hydrogen,” so when oxygen is added or hydrogen is removed to a molecule, the molecule is being oxidized.
The reverse of this is called
reduction. Reduction is defined as “adding of hydrogen,” or “removing of
oxygen,” so when hydrogen is added or oxygen is removed to a
molecule, the molecule is being reduced.
2Na + H2 +Heat → 2NaH (Reduction)
CuO +H2 → Cu+H2O
In this reaction oxidation and
reduction chemical reaction take place simultaneously. It is called Redox
reaction.
Frequently Asked Questions
Q: What is the left side of the chemical formula called?
Ans : Reactants/RegaentsQ: What is the right side of the chemical formula called?
Ans : ProductsQ: What is left over in a chemical reaction?
Ans : Reactants/RegaentsQ: What is the major reason for reaction to occur?
Ans : Chemical reactions occur so that the atoms of the elements of reactants will become more stable.Q: How do you identify a chemical reaction?
Ans : There are some easy ways to detect a chemical reaction:(a) Change in Color.
(b) Precipitate Formation. (solid formation falling out of solution)
(c) Gas Formation. (bubbles and odor)
(d) Temperature Change.
Q: Why do we need to balance a chemical reaction?
Ans : The law of conservation of mass states that matter can neither be created nor destroyed so a chemical equation should always be balanced.Q: What is called an unbalanced chemical equation?
Ans : Skeletal equationQ: Give example of chemical reaction that release heat.
Ans : Calcium oxide reacts vigorously with water to produce slaked lime (calcium hydroxide) releasing a large amount of heat.CaO(s) + H2O(l) → Ca(OH)2(aq)+Heat
Q: What is exothermic reaction?
Ans : Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.Q: Give example of chemical reaction that absorb heat.
Ans : Plants absorb heat energy from sunlight to convert carbon dioxide and water into glucose and oxygen.6CO2+6H2O+Heat→C6H12O6+CO2
Q: Give example of chemical reaction that release gas.
Ans : When zinc reacts with sulphuric acid, hydrogen gas is evolved with the formation of zinc sulphate.Zn + H2SO4 → ZnSO4 + H2
Q: Give example of chemical reaction that change colour.
Ans : When iron nail is dipped into copper sulphate solution ,iron nail become brownish in colour and the blue colour of copper sulphate solution fade (green).Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)
Q: Give example of chemical reaction that produce precipitate.
Ans : When silver nitrate and potassium chloride react, A white precipitate of silver chloride is formed.AgNO3(aq) + KCl (aq)→ AgCl (s) (↓) + KNO3 (aq)
