Hello students, in this article we are going to show you notes of chapter Chemical Reactions and Equations. This is notes of chapter 1 class 10 science.
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| Class 10 science chapter 1 notes |
Notes of Chemical Reactions and Equations class 10 science:-
Chapter 1 science:- chemical Reactions and Equations
Chemical Reaction:-a new substance is formed in a chemical reaction which is completely different in properties from the original substance. Only a rearrangement of atoms take place in a chemical reaction.
• for example:- burning of magnesium in the air to form magnesium oxide.
2mg(s) + O2(g) ∆--------- 2mgO(s)
Reactant:- this is the substances which takes part in a chemical reaction.
Example:- Mg and O2
Product:- New substance that is formed after a chemical reaction.
Example:- MgO
Characteristics of chemical reactions:-
A chemical reactions can show one or more characteristics
1. Evolution of gases
2. Change in colour
3. Change in state of substance
4. Change in temperature
5. Formation of precipitate
Chemical Equation:- representation of chemical reaction using symbols and formula of the substances
A+B-------C+D
A and B are called reactants and C and D are called the products. The arrow shows the direction of the chemical reaction.
For example: Hz (g) + O2 (g) + H2O (1)
A chemical equation becomes more informative by writing the states of substances:
•Gaseous state is represented by symbol (g).
•Liquid state is represented by symbol (1).
•Solid state is written by symbol (s). •Aqueous solution is written by symbol (aq).
•Reagent/catalyst/ temperature /pressure /reaction conditions are written generally above the arrow.
Balanced Chemical Equation: A balanced chemical equation has the number of atoms of each element equal on both sides.
Example: Zn + H2SO4+ ZnSO4 + H2
In this equation, numbers of zinc, hydrogen and sulphate are equal on both sides, so it is a Balanced Chemical Equation.
Type's of Chemical Reactions:
Chemical reactions can be classified in following types:
1. Combination Reaction
Reactions in which two or more reactants combine to form one product.
A + B------------ AB
Examples:
1. Magnesium +Oxygen----Magnesium Oxide Mg(s)+ O2(g) + 2MgO(s)
2. Decomposition reaction
Reactions in which a single compound broke down to give two or more simpler substance.
AB------------ A + B
A decomposition reaction is just the opposite of combination reaction.
Examples:
1. When calcium carbonate is heated, it decomposes into calcium oxide and carbon dioxide.
CaCO(s) heat-CaO(s)+ CO(g)
Calcium carbonate Calcium oxide + Carbon dioxide
2. When ferrous sulphate is heated, it decomposes into ferric oxide sulphur dioxide and sulphur trioxide
2FeSO,(s) Fe,O,(s)+ SO, (g) + SO (0)
Three types of decomposition reactions:
• Thermal Decomposition reaction
when the decomposition take place due to heat is called thermal decomposition reaction.
Example:-
2Pb(No3)2(S) ∆-------2PbO(S) +4NO2(g)+ O2(g)
• Electrolytic decomposition Reaction
When the decomposition take place due to electricity is called Electrolytic decomposition reaction or electrolysis.
Example:-
When electricity is passed in water it decomposes into hydrogen and oxygen.
2H2O(I)---------2H2(g) + O2(g)
• photolysis or photo decomposition reaction
when the decomposition take place in the presence of sunlight is called photolysis or photo decomposition reaction.
Example:-
When silver chloride is put in sunlight at decomposes into silver metal and chlorine gas.
2AgCl(S)(white)sunlight-----2Ag(s)grey+cl2(g)
3. Displacement reaction
the chemical reaction in which a more reactive element displaces are less reactive element from a compound is known as displacement reaction.
• displacement reactions are also known as substitution reaction or single displacement reaction
Example:
A + BC ----------AC + B
Zn(s)+Cuso4(aq)-------Znso4(aq)+Cu(s)
4. Double displacement reaction
reactions in which ions are exchanged between two reactants forming new compounds are called double displacement reactions.
AB + CD ------------- AC + BD
Example:-
when the solution of barium chloride react with the solution of sodium sulphate, white precipitate of barium sulphate is formed along with sodium chloride.
Bacl2(aq)+Na2So4(aq)----- Baso4(precipitate) + 2Nacl(aq)
5. Redox Reaction
• Oxidation
Addition of oxygen (non metal )removal of hydrogen (metal)from a compound is called oxidation reaction.
• elements or compounds in which oxygen / hydrogen / metal is removed are called to be oxidized.
• the substance which get oxidised is the reducing agent.
• Reduction
addition of hydrogen / metal or removal of oxygen or nonmetal from a compound is called reduction reaction.
•elements or compounds in which hydrogen/ metal is added or oxygen or nonmetal is removed are called to be reduced.
• the substance which gets reduced is the oxidizing agent.
Oxidation and Reduction take place together. The reaction in which oxidation and reduction both take place simultaneously is called Redox reaction.
CuO+H₂ ------------Cu + H2O
•In this reaction, CuO is changing into Cu. Oxygen is being removed from copper oxide. So, copper oxide is being reduced to copper.
•In this reaction, H₂ is changing to H2O. Oxygen is being added to hydrogen. So hydrogen is being oxidised to water.
6. Exothermic and Endothermic Reactions:
Exothermic Reaction:
Reaction which produces heat energy is called Exothermic Reaction. Most of the decomposition reactions are exothermic.
Example: 1. Respiration is a exothermic reaction in which energy is released when glucose reacts with oxygen to form water and CO2
C&H12O6 (aq) + 602(g)--------6H2O(1)+6CO2(g)+heat energy
2. When quick lime (CaO) is added to water, it releases energy.
CaO (s) + H2O(1) -----Ca(OH)2 (aq)+ ENERGY
Endothermic Reaction:
A chemical reaction in which heat energy is absorbed is called Endothermic Reaction.
Example:
1. Decomposition of calcium carbonate.
CaCO3 (s) + heat CaO (s)+ CO2 (g) + ENERGY
Corrosion: It is an undesirable change that occurs in metals when they are attacked by moisture, air, acids and bases. Example: Rusting of iron, corrosion of copper
a) Rusting of iron: Iron when reacts with oxygen and moisture forms red substance which is called Rust.
4Fe(s)+ 302(g) + H20(1) ------2Fe2O3.xH2O (s)
Corrosion of Copper: Copper objects lose their lustre and shine after some time because the surface of these objects acquires a green coating of basic copper carbonate, CuCO3.Cu(OH)2 when exposed to air.
2Cu(s) + CO2 (g) + O2(g) + H2O(l) ------- CuCOs.Cu(OH)2 (s)
Corrosion of Silver Metal: The surface of silver metal gets tamished (becomes dull) on exposure to air, due to the formation of a coating of black silver sulphide (Ag₂S) on its surface by the action of HS gas present in the air.
2Ag(s) + H2S (g) → AgǝS(g)+ H2(g)
Rancidity:
The taste and odour of food materials containing fat and oil changes when they are left exposed to air for a long time. This is called Rancidity. It is caused due to the oxidation of fat and oil present in food materials.
Methods to prevent rancidity:
•By adding anti-oxidants.
• Vacuum packing/ storing in air-tight container.
•Replacing air by nitrogen.
•Refrigeration of foodstuff.
