CBSE Class 10 Science Chapter 1 (Chemical Reactions and Equations) Notes
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CHAPTER 1- CHEMICAL REACTIONS AND EQUATIONS
The process in which new substances with new properties are formed from one or more substances is called Chemical Reaction. The substances which take part in chemical reaction are called Reactants. The substances which are formed in a chemical reaction are called Products.
(i) Digestion of food
(iii) Rusting of iron
(iv) Burning of Magnesium ribbon
(v) Formation of curd
Chemical reaction involves :
- Change in state
- Change in colour
- Change in temperature
- Evolution of gas
A chemical reaction can be represented by chemical equation. It involves uses of symbol of elements or chemical formula of reactant and product with mention of physical state.
The necessary conditions such as temperature, pressure or any catalyst should be written on arrow between reactant and products. e.g., Magnesium is burnt in air to form magnesium oxide. 2Mg +O2→2MgO
Types of Chemical Reactions
|S NO||Types of reactions||Examples|
A single product is formed from two or more reactants.
A single reactant breaks down to yield two or more products.
i) Thermal decomposition
2Pb(NO3)2 → 2PbO + 4NO2 +O2
|ii) Electrolysis||2H2O →2H2 +O2|
|iii) Photo chemical reaction||2AgBr →2Ag +Br2|
One element is displaced by another element.
Zn + CuSO4→ ZnSO4 + Cu
|4||Double displacement reaction
Exchange of ions between reactants.
AgNO3 +NaCl →AgCl +NaNO3
Both oxidation and reduction take place simultaneously
CuO + H2 → Cu + H2O
- 4. i)Exothermic reaction:A chemical reaction in which heat energy is evolved.
C + O2 →CO2 (g) + heat
ii)Endothermic reaction:A chemical reaction in which heat energy is absorbed.
ZnCO3 + Heat →ZnO + CO2
5 .Redox reaction:Chemical reaction in which both oxidation and reduction take place simultaneously.
Oxidation:Reaction that involves the gain of oxygen or loss of hydrogen.
Reduction:Reaction that shows the loss of oxygen or gain of hydrogen
ZnO + C →Zn + CO
ZnO is reduced to Zn -reduction
C is oxidized to CO ——oxidation
Effects of oxidation reactions in our daily life:
a) Corrosion: It is an undesirable change that occurs in metals, when they are attacked by moisture, air, acids and bases.
Corrosion (rusting) of iron: Fe2O3. xH2O (Hydrated iron oxide)
Corrosion of copper:CuCO3.Cu (OH) 2 (Basic copper carbonate)
Corrosion of silver:Ag2S (Silver sulphide)
Corrosion of Aluminum: Al2O3 (Aluminum oxide)
b) Rancidity: Undesirable change that takes place in oil containing food items due to the oxidation of fatty acids.
(1)Adding antioxidants to the food materials.
(2) Storing food in air tight container
(3) Flushing out air with nitrogen gas.
CBSE Science Class 10 Ch. 1 Important Questions with Answers (only hints)
Very short answer questions. (1 mark)
- Identify in the following reaction:
2PbO +C→2Pb +CO
- the substance oxidised and
- the substance reduced.
- A shiny brown coloured element “x” on heating in air becomes black in
colour . Name the element “x” and the black coloured compound formed.
Ans: Element ‘x’is Copper and the black coloured compound is cupric oxide Cu2O
Short answer type questions (2 mark)
- Classify the following reaction as combination,decomposition,displacement and double displacement reaction:-
a)BaCl2 +H2SO4 → BaSO4 +2HCl
Ans: Double displacement reaction.
- b) 3CuSO4+ 2Al→ Al2 (SO4)3 +3Cu
1. c)ZnCO3 →ZnO +CO2
Ans: Decomposition reaction
- d) C +O2→CO2
Q.2. What is a precipitation reaction? Give an example.
Ans. Reaction in which an insoluble substance or precipitate is formed Na2 + BaCl2————BaSO4+2NaCl
Short answer type questions (3 mark)
- Give an example, each for thermal decomposition and photochemical decomposition reactions. Write balanced equation for the same.
Ans.Thermal decomposition – Heating of lime stone. CaCO3→CaO +CO2
Photochemical decomposition – Action of light on silver bromide.
2 AgBr→2Ag +Br2
VALUE BASED QUESTION
Jonali visited her grandmother during summer holidays.Her grandmother prepared chips for her and stored it in airtight containers.
- a) What value is shown by her grandmother?
- b) Why did Jonali’s grandmother store the snack in airtight container?
Ans: a) Scientific temperament / concern for health
- b) Toprevent the food items from rancidity.
Very long answer type questions (5 mark)
- (i) Write chemical equations for the following and balance them.
- a) Zinc carbonate(s) →Zinc oxide+ Carbon dioxide
Ans) ZnCO3 →ZnO +CO2
- b) Potassium bromide(aq) + Barium iodide(aq)→ Potassium iodide + Barium bromide.
Ans) 2KBr + BaI2 → 2KI + BaBr2
- Nitrogen + Hydrogen → Ammonia
Ans) N2 + 3H2 → 2NH3
- ii) What happens when electricity is passed through acidified water ?
Decomposition of water takes place resulting in the formation of hydrogen and oxygen.