Thu May 27, 2010 12:01 am
Imp Question from Chemical reactions and Equations
Q.1 what do we observe when magnesium ribbon burns in air?
Ans. magnesium ribbon burns in air(oxygen) with a dazzling white flame and changes into a white powder(magnesium oxide).
Q.2 what are the possible changes that can be observed during a chemical change?
Ans. The Possible changes are :
1. change in state
2. change in colour
3. evolution of a gas
4. change in temperature
5. formation of precipitate
Q.3 what are reactants and products?
Ans. - the substances that undergo chemical change in the reaction are called reactants.
- The new substances formed during the reaction are called products.
Q.4 what does the arrowhead towards the products in a chemical reaction show?
Ans. the arrowhead towards the products in a chemical reaction shows the direction of the reaction.
Q.5 what is a chemical equation?
Ans. a chemical equation is an equation that represents a chemical reaction.
Q.6 what is skeletal chemical equation?
Ans. skeletal chemical equation is the chemical equation in which the reactants and the products are not balanced.
Q.7 what is the need to balance a chemical equation?
Ans. chemical equation needs to be balanced so that it follows the law of conservation of mass, i.e., the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants.
Q.8 state the law of conservation of mass.
Ans. mass can neither be created nor destroyed in a chemical reaction.
Q.9 what are the notations for gaseous, liquid, aqueous and solid states of substances in a chemical equation?
Ans. the gaseous, liquid, aqueous and solid states of substances in a chemical equation are represented by the notations (g), (l), (aq) ans (s), respectively.
Q.10 where are the reaction conditions like temperature, pressure, catalyst etc. indicated in a chemical equation?
Ans. the reaction conditions like temperature, pressure, catalyst, etc are indicated above and/or below the arrow in the equation.
Q.11 what does chemical reaction involve?
Ans. chemical reaction involves breaking and making of bonds between atoms to produce new substance(s).
Q.12 what are combination reactions?
Ans. the reactions in which two or more substances react to form a single product are called combination reactions. e.g,
1. burning of coal
2. formation of water from hydrogen and oxygen
3. Burning of magnesium to form magnesium oxide.
Q.13 what are exothermic reactions? Give examples.
Ans. reactions in which heat is released along with the formation of products are called exothermic chemical reactions. e.g,
1. burning of natural gas
2. respiration
3. decomposition of vegetable matter into compost
4. adding water to calcium oxide to form slaked lime(calcium hydroxide).
5. dilution of acids.
Q.14 why is respiration exothermic?
Ans. -in respiration carbohydrates are broken down to glucose which combines with oxygen to provide energy.
-this energy makes respiration exothermic.
Q.15 what is decomposition reaction?
Ans. a reaction in which a single substance breaks down to form two or more substances is called a decomposition reaction. e.g,
1. electrolysis of water
2. decomposition of calcium carbonate to calcium oxide and carbon dioxide.
Q.16 what happens when ferrous sulphate is heated in a dry boiling tube?
Ans. (refer to ncert pg 8, the equation and the paragraph below it)
Q.17 what is quick lime? give one of its use.
Ans. -quick lime is the general name for calcium oxide.
- it is used in the manufacture of cement.
Q.18 what is thermal decomposition.
Ans. when a decomposition reaction is carried out by heating, it is called thermal decomposition. e.g.,
1. heating of limestone(calcium carbonate) to form quick lime and carbon dioxide.
2. heating lead nitrate powder to form lead oxide, nitrogen oxide and oxygen.
Q.19 What are endothermic reactions?
Ans. reactions in which energy is absorbed are known as endothermic reactions. e.g,
1. heating of limestone(calcium carbonate) to form quick lime and carbon dioxide.
2. heating lead nitrate powder to form lead oxide, nitrogen oxide and oxygen.
Q.20 what is displacement reaction?
Ans. when one element displaces another element from its solution, the reaction is known as displacement reaction. e.g,
1. reaction of iron and copper sulphate to form iron sulphate and copper.
2. displacement of copper from copper sulphate by zinc.
Q.21 what is precipitate?
Ans. the insoluble substance formed during a chemical reaction is called precipitate.
Q.22 what is a precipitation reaction?
Ans. a reaction that produces a precipitate is called a precipitation reaction. e.g,
Na2SO4 (aq) + BaCl2 ------> BaSO4 (s) + 2NaCl (aq)
here BaSO4 is a precipitate.
Q.23 what are double displacement reactions?
Ans. the reactions in which there is an exchange of ions between the reactants are called double displacement reactions. e.g,
Na2SO4 (aq) + BaCl2 ------> BaSO4 (s) + 2NaCl (aq)
Q.24 when is a substance oxidised and reduced?
Ans. - if a substance gains oxygen or loses hydrogen during a reaction, it is said to be oxidised.
- if a substance loses oxygen or gains hydrogen during a reaction, it is said to be reduced.
Q.25 what are redox reactions?
Ans. -the reactions in which one substance gets oxidised and the other substance gets reduced, are called redox reactions.
-here ‘red’ stands for reduction and ‘ox’ stands for oxidation.
Q.26 what do you mean by oxidising and reducing agents?
Ans. - the substances which get reduced to oxidise other substances in reactions are called oxidising agents.
- the substances which get oxidised to reduce other substances in reactions are called reducing agents.
Q.27 what do you mean by corrosion?
Ans. when a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion.
Q.28 what are antioxidants?
Ans. substances which prevent rancidity are called antioxidants.
Q.29 what is rancidity?
Ans. The change in the smell and taste of fats and oils due to oxidation is called rancidity.
Q.30 how are chips prevented from oxidation?
Ans. the bags of chips are flushed with nitrogen to prevent the chips from getting oxidised.
Ans. magnesium ribbon burns in air(oxygen) with a dazzling white flame and changes into a white powder(magnesium oxide).
Q.2 what are the possible changes that can be observed during a chemical change?
Ans. The Possible changes are :
1. change in state
2. change in colour
3. evolution of a gas
4. change in temperature
5. formation of precipitate
Q.3 what are reactants and products?
Ans. - the substances that undergo chemical change in the reaction are called reactants.
- The new substances formed during the reaction are called products.
Q.4 what does the arrowhead towards the products in a chemical reaction show?
Ans. the arrowhead towards the products in a chemical reaction shows the direction of the reaction.
Q.5 what is a chemical equation?
Ans. a chemical equation is an equation that represents a chemical reaction.
Q.6 what is skeletal chemical equation?
Ans. skeletal chemical equation is the chemical equation in which the reactants and the products are not balanced.
Q.7 what is the need to balance a chemical equation?
Ans. chemical equation needs to be balanced so that it follows the law of conservation of mass, i.e., the total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the elements present in the reactants.
Q.8 state the law of conservation of mass.
Ans. mass can neither be created nor destroyed in a chemical reaction.
Q.9 what are the notations for gaseous, liquid, aqueous and solid states of substances in a chemical equation?
Ans. the gaseous, liquid, aqueous and solid states of substances in a chemical equation are represented by the notations (g), (l), (aq) ans (s), respectively.
Q.10 where are the reaction conditions like temperature, pressure, catalyst etc. indicated in a chemical equation?
Ans. the reaction conditions like temperature, pressure, catalyst, etc are indicated above and/or below the arrow in the equation.
Q.11 what does chemical reaction involve?
Ans. chemical reaction involves breaking and making of bonds between atoms to produce new substance(s).
Q.12 what are combination reactions?
Ans. the reactions in which two or more substances react to form a single product are called combination reactions. e.g,
1. burning of coal
2. formation of water from hydrogen and oxygen
3. Burning of magnesium to form magnesium oxide.
Q.13 what are exothermic reactions? Give examples.
Ans. reactions in which heat is released along with the formation of products are called exothermic chemical reactions. e.g,
1. burning of natural gas
2. respiration
3. decomposition of vegetable matter into compost
4. adding water to calcium oxide to form slaked lime(calcium hydroxide).
5. dilution of acids.
Q.14 why is respiration exothermic?
Ans. -in respiration carbohydrates are broken down to glucose which combines with oxygen to provide energy.
-this energy makes respiration exothermic.
Q.15 what is decomposition reaction?
Ans. a reaction in which a single substance breaks down to form two or more substances is called a decomposition reaction. e.g,
1. electrolysis of water
2. decomposition of calcium carbonate to calcium oxide and carbon dioxide.
Q.16 what happens when ferrous sulphate is heated in a dry boiling tube?
Ans. (refer to ncert pg 8, the equation and the paragraph below it)
Q.17 what is quick lime? give one of its use.
Ans. -quick lime is the general name for calcium oxide.
- it is used in the manufacture of cement.
Q.18 what is thermal decomposition.
Ans. when a decomposition reaction is carried out by heating, it is called thermal decomposition. e.g.,
1. heating of limestone(calcium carbonate) to form quick lime and carbon dioxide.
2. heating lead nitrate powder to form lead oxide, nitrogen oxide and oxygen.
Q.19 What are endothermic reactions?
Ans. reactions in which energy is absorbed are known as endothermic reactions. e.g,
1. heating of limestone(calcium carbonate) to form quick lime and carbon dioxide.
2. heating lead nitrate powder to form lead oxide, nitrogen oxide and oxygen.
Q.20 what is displacement reaction?
Ans. when one element displaces another element from its solution, the reaction is known as displacement reaction. e.g,
1. reaction of iron and copper sulphate to form iron sulphate and copper.
2. displacement of copper from copper sulphate by zinc.
Q.21 what is precipitate?
Ans. the insoluble substance formed during a chemical reaction is called precipitate.
Q.22 what is a precipitation reaction?
Ans. a reaction that produces a precipitate is called a precipitation reaction. e.g,
Na2SO4 (aq) + BaCl2 ------> BaSO4 (s) + 2NaCl (aq)
here BaSO4 is a precipitate.
Q.23 what are double displacement reactions?
Ans. the reactions in which there is an exchange of ions between the reactants are called double displacement reactions. e.g,
Na2SO4 (aq) + BaCl2 ------> BaSO4 (s) + 2NaCl (aq)
Q.24 when is a substance oxidised and reduced?
Ans. - if a substance gains oxygen or loses hydrogen during a reaction, it is said to be oxidised.
- if a substance loses oxygen or gains hydrogen during a reaction, it is said to be reduced.
Q.25 what are redox reactions?
Ans. -the reactions in which one substance gets oxidised and the other substance gets reduced, are called redox reactions.
-here ‘red’ stands for reduction and ‘ox’ stands for oxidation.
Q.26 what do you mean by oxidising and reducing agents?
Ans. - the substances which get reduced to oxidise other substances in reactions are called oxidising agents.
- the substances which get oxidised to reduce other substances in reactions are called reducing agents.
Q.27 what do you mean by corrosion?
Ans. when a metal is attacked by substances around it such as moisture, acids, etc., it is said to corrode and this process is called corrosion.
Q.28 what are antioxidants?
Ans. substances which prevent rancidity are called antioxidants.
Q.29 what is rancidity?
Ans. The change in the smell and taste of fats and oils due to oxidation is called rancidity.
Q.30 how are chips prevented from oxidation?
Ans. the bags of chips are flushed with nitrogen to prevent the chips from getting oxidised.
