|
Decomposition Reactions |
AB -> A + B, e.g. CaCO3-> CaO + CO2, They are
endothermic |
|
Displacement Reaction |
AB + C -> AC + B e.g. Fe + CuSO4 -> FeSO4 + Cu.
They are based on reactivity series: Na>
Ca> Al > Zn> Fe > Cu > Ag > Au |
|
Double Displacement Reaction |
AB + CD -> AC + BD, e.g. Na2SO4 + BaCl2 -> NaCl +
BaSO4. They form precipitates at the bottom of test tubes |
|
Oxidation-Reduction Reaction |
AO + H2 -> A + H2O e.g. CuO + H2 -> Cu + H2O. They
are also called Redox reactions. |
|
Corrosion |
Iron form Reddish brown powder, Silver forms black
coating, Copper forms green colour coating due to corrosion |
|
Rancidity |
They foods containing oils and fats turn sour by
reacting with oxygen present in air. Rancidity is prevented by flushing such foods
with gases like nitrogen |
Ans: The method of representing chemical reaction with the help of formula of substances involved is called chemical equation. Eg,
Zn + H2SO4 -----------> ZnSO4 + H2
BALANCING OF EQUATION:
A balanced equation is a chemical equation which has equal number of atoms in reactants as well as products.
An equation is balanced by hit and trail method. First skeleton equation is written
eg H2 + O2 ----------> H2O
Then, number of atoms on both sides of equation are counted. In above equation,
2 atoms of H and O are reacting, to give 2 atom of H and 1 atom of O.
Lastly, the atoms on both sides of equation are made equal by hit and trail method
2 H2 + O2 ----------> 2 H2O
Q. What is combination reaction. Give example of combination reaction.
Ans: A reaction in which two or more substances, elements or compounds combine to form single substance is called combination reaction.
Examples of combination reaction:
2 H2 + O2 ---------> 2 H2O
Hydrogen oxygen water
CaO + CO2 ----------> CaCO3
Q. Why should chemical equation be balanced?
Ans: A balanced chemical equation is one that has the same number of atoms of each element in the reactants as in the products.
The chemical equation needs to be balanced so that it follows the law of conservation of mass so that mass of products should be equal to mass of reactants.
Q. What is decomposition reaction? Give examples.
Ans: The reaction in which a compound splits up into two or more simple substances is called decomposition reaction.
It is carried out by heat, light or electricity
Examples of decomposition reaction:
CaCO3 ------------------> CaO + CO2
calcium carbonate Calcium oxide carbon dioxide
Q. What is displacement reaction? Give examples.
Ans: The reaction in which one element takes place of another in a compound is called displacement reaction.
In a Displacement reaction, a more reactive element displaces a less reactive element.
Example of displacement reaction:
CuSO4 + Zn ----------> ZnSO4 + Cu
Copper sulphate zinc zinc sulphate copper
The zinc replaces copper from copper sulphate because it is more reactive than copper.
Q. What is double displacement reaction? Give examples.
Ans: The reaction in which two componds react by exchange of ions to form new compounds is called double displacement reaction.
In this reaction, one product which is insoluble precipitates down.
Example of Double displacement reaction:
AgNO3 + NaCl -------> AgCl + NaNO3
Silver nitrate sodium chloride silver chloride sodium nitrate
Q. What is oxidation Reduction reaction. Give examples.
Or
What is redox reaction
Ans: Oxidation Reduction reaction is also known as redox reaction. It is the reaction where addition of oxygen/ removal of hydrogen or vice versa takes place simultaneously.
It is also defined as reaction where one substance looses electron and other substance gains electron.
Examples of Redox reaction:
CaO + H2 ----------> Cu + H2O
Copper oxide Hydrogen Copper Water
In this reaction, Copper oxide is reduced to Copper i.e removal of oxygen and Hydrogen is oxidized to form water i.e addition of oxygen
Q. Differentiate between combination reaction and
decomposition reaction with the help of examples
Ans:
|
Combination Reaction |
Decomposition Reaction |
|
Two or more reactant form single product |
A single reactant forms two or more products |
|
They are usually exothermic |
They are usually endothermic |
|
e.g 2Mg + O2 -> 2 MgO |
e.g. CaCO3 -> CaO + CO2 |
Q. Write a balanced chemical equation for the following chemical reactions:
i. Barium Chloride + Aluminium sulphate -> Barium sulphate + Aluminium chloride
3 BaCl2 + Al2(SO4)3 -> 3 BaSO4 + 2 AlCl3
ii. Zinc carbonate -> Zinc Oxide + Carbon dioxide
ZnCO3 -> ZnO + CO2
Q. What would you observe when zinc is added to a solution of Iron (II) sulphate? Write a chemical reaction that takes place.
Ans: When Zinc is added to the iron sulphate solution, the zinc displaces iron to form Zinc Sulphate.
The reaction can be written as:
FeSO4 + Zn -> ZnSO4 + Fe
i. CaO + H2O -> Ca(OH)2
Ans: Combination Reaction
ii. BaCl2 + Al2(SO4)3 -> AlCl3 + BaSO4
Ans: Double Displacement Reaction
iii. FeSO4 -> Fe2O3 + SO2 + SO3
Ans: Decomposition Reaction
Q. Write the balanced equation for the following reactions:
(a) Hydrogen + Chlorine → Hydrogen chloride
Ans: H2 + Cl2 -> 2HCl
(b) Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
Ans: 3BaCl2 + Al2(SO4)3 → 2AlCl3 + 3BaSO4
(c) Sodium + Water → Sodium hydroxide + Hydrogen
Ans: 2Na + 2H2O → 2NaOH + H2
Q. Decomposition reactions require energy either in the form of heat or light or electricity for breaking down the reactants. Write one example of each form.
Ans: The reaction in which a compound splits up into two or more simple substances is called decomposition reaction.
Examples:
Heat: CaCO3 -> CaO + CO2
Light: AgCl -> Ag + Cl2
Electricity: H2O -> H2 + O2
TEXTUAL QUESTIONS
Q. A solution of substance "X" is used for white washing.
a. Name the substance X and write its formula.
b. How will the substance X react with water.
Ans:
A. The substance X is calcium oxide, Its formula is CaO
B. The reaction of substance X with water will be;
CaO + H2O -------> Ca(OH)2
Q. Why should a magnesium ribbon be cleaned before burning in air?
Ans: Magnesium is very reactive and should be cleaned before burning to remove the Magnesium oxide layer from the ribbon which slows down the burning of magnesium ribbon.
Q. Why does the colour of copper sulphate change when iron nail is dipped in it.
Ans: When iron reacts with copper sulphate, it displaces copper from copper sulphate solution,
CuSO4 + Fe ----------> FeSO4 + Cu
In this displacement reaction, the blue colour of copper sulphate fades away and green colour is formed.
Q. What is balanced chemical equation. Why should a chemical equation be balanced.
Ans: Balanced chemical equation is a type of equation in which there are equal amount of atoms in reactants and products.
The chemical equation should be balanced because of law of conservation of mass. It states that mass of reactants should be always equal to mass of products.
Q. What is Exothermic reaction and Endothermic reaction.
Ans: Exothermic reaction is a type of reaction in which heat is given out. In other words energy is produced. E.g
C + O -------------> CO2
Endothermic reaction is a type of reaction in which heat is absorbed. In other words energy is needed for reaction to take place. E.g
N2 + O2 -----------> 2NO
Q. What is Precipitation reaction?
Ans: Precipitation reaction is double displacement reaction. In this reaction, two compounds react by exchange of ions and an insoluble product is formed. This insoluble product is also called as precipitate. E.g,
AgNO3 + NaCl --------> AgCl + NaNO3
Silver nitrate Sodium chloride Silver chloride Sodium nitrate
Q. Why do we apply paint on iron articles.
Ans: Iron reacts with oxygen in presence of moisture to form rust. The process is also called corrosion.
To prevent direct contact of iron with oxygen, Iron articles are painted.
Q. What is rancidity? Why are foods flushed with Nitrogen gas?
Ans: Rancidity is a process in which foods made of oils and fats get oxidized. This is characterized by bad smell and taste.
The food containing fats and oils are flushed with unreactive nitrogen gas, so there is no availability of oxygen to cause oxidation.
Q. What is Corrosion?
Ans: Corrosion is a process in which metals are consumed by action of oxygen in presence of moisture.
Corrosion weakens the metals smd structures made of metals.
E.g, During the corrosion of iron, Iron metal is oxidized to form rust
4 Fe + 3 O2 + H2O ------> 2Fe2O3.H2O
Q. A shiny brown colour element "X" on heating turns black. Name the element and why it turns black
Ans: The element "X" is COPPER, (Cu)
When copper is heated it reacts with oxygen to form copper oxide which is black in colour.
2 Cu + O2 ------> 2 CuO
Copper Oxygen Copper Oxide
a. Zn + CusO4 ----Ã ZnSO4 + Cu
b. Na + O2 ----Ã Na2O
c. HNO3+ Ca(OH)2 ---Ã Ca(NO3)2 + H20
Ans:
a. Zn + CusO4 ----Ã ZnSO4 + Cu
b. 4Na + 02 ----Ã 2Na20
2 HNO3+ Ca(OH)2 ---> Ca(NO3)2 + 2 H20
Objective Type Questions:
A. Burning of magnesium in air
B. Digestion of food in our body
C. Melting of Ice
D. Turning brown of a freshly cut apple.
Ans: C. Melting of Ice
Q. Write the balanced equation for reaction involving decomposition of calcium carbonate into calcium oxide and carbon dioxide?
Ans: The chemical equation is as follows;
CaCO3(s)→CaO(s)+CO2(g)
Q. Barium chloride reacts with sodium sulphate to form barium sulphate and sodium chloride,
BaCl2 + Na2SO4 _____> BaSO4 + NaCl
The above reaction is an example of:
A. Combination reaction
B. Decomposition reaction
C. Displacement reaction
D. Double displacement reaction
Ans: D. Double displacement reaction.
Q. Write a balanced chemical equation for a reaction involving the combination between hydrogen and chlorine to form hydrogen chloride.
Ans:
The balanced equation is:
H2 (g) +Cl2 (g) →2HCl (g)
Q. Write a balanced chemical equation for the reaction involving displacement of hydrogen from sulphuric acid by zinc to form zinc sulphate and hydrogen gas.
Ans: The balanced equation is;
Zn(s) + H2SO4(aq) —-> ZnSO4(aq) + H2(g)
Q. When the calcium carbonate is heated, ut gives calcium oxide and carbon dioxide.
CaCO3 ______> CaO + CO2
This reaction is an example of :
A. Combination reaction
B. Decomposition reaction
C. Displacement reaction
D. Double displacement reaction
Ans: B. Decomposition reaction
Q. Which of the statements about the reaction below are incorrect?
2PbO (s) + C (s) ------------> 2Pb (s) + CO2 (g)
a.) Lead is getting ready.
b.) Carbon dioxide is getting oxidised.
c.) Carbon is getting oxidised.
d.) Lead oxide is being reduced.
Answer:- a and b
Lead is getting reduced and
Carbon dioxide is getting oxidised.
Q. Fe2O3 + 2Al -----------> AlO3 + 2Fe.
The above reaction is an example of a;
a.) combination reaction.
b.) double displacement reaction
c.) decomposition reaction
d.) displacement reaction
Answer:- Displacement reaction.
a.) Reduction
b.) Oxidation
c) Redox reaction
d.) None of these
Answer:- Reduction
Q. Which of the following is not a chemical reaction?
a.) Souring of milk
b.) Dissolution of sugar in water
c.) Rusting of iron
d.) Digestion of food
Ans.:- Dissolution of sugar in water.
Q. which of the following methods is suitable for preventing an iron frying pan from rusting?
b.) Applying paint
c.) Applying coating of zinc
d.) All of these.
Ans:- Applying coating of zinc.
Q. The correct formula of rust is;
a.) Fe2O3
b.) Fe3O4
c.) Fe2O3 xH2O
d.) Fe3O4 xH20
Ans.:- Fe2O3--xH20
Q. Rancidity occurs when oils and fats are;
c.) Decomposed d.) None
Ans:-Oxidised
Q. when lime stone is heated, the chemical reaction that takes place;
a.) Decomposition b.) Combination
c.) Electrolysis d.) Displacement.
Ans: Decomposition
Q. 2KClO3 ----------------> 2KCl + 3O2 is a;
a.) Decomposition reaction
b.) Combination reaction
c.) Displacement rection
d.) Isomerisation reaction
Ans:--- Decomposition reaction
Q. Rusting is ;
a.) Reducing reaction
b.) Decomposition reaction
c.) Oxidation reaction
d.) Redox reaction
Ans:--- Redox reaction
Q. The reaction in which heat energy is given out is called;
a.) Endothermic b.) Exothermic
c.) Isomerisation d.) None
Q. Consider the reaction
Which reaction is it?
b.) Double decomposition reaction
c.) Combination reaction
d.) Displacement reaction
Ans:--- Double decomposition reaction
Q. Which is an exothermic reaction?
a.) C+O2 -------> CO2 +394 KJ
b.) N2 + O2 --------> 2NO +330 KJ
c.) CaCO3----------> CaO + CO2-- Heat
d.) None of these.
Ans:--- C+ O2------> CO2 + 394 KJ
Q. ZnO +C -------> Zn + CO
The above given reaction is an example of;
a.) Oxidation b.) Reduction
c.) Redox Reaction d.) Combination reaction
Ans:- Redox reaction
Q. In order to balance the following chemical equation, the value of Cofficients x and y resp. are
xpb( NO3)2 Heat > 2Pbo + yNo2 + O2
a) 2, 4 b) 2, 2 c) 2, 3 d) 4, 2
Ans: a) 2, 4
2Pb( NO3)2 Heat > 2Pbo + 4NO2 + O2
Ans:
sunlight
2AgCl(s) ----------------> 2Ag (s)+Cl2(g)
Q. Which of following processes involves chemical reactions?
a. Storing oxygen gas under high pressure
b. Liquification of air
c. Keeping petrol in china dish in open
d. Heating copper wire in presence of air
Ans: D: Heating copper wire in presence of air.
Q. Assertion: When zinc is dipped in copper sulphate solution, reddish brown particles at the botton
Reason: Zinc displaces copper to form zinc sulphate, and reddish brown particles of copper settle at bottom
Ans: Both are correct, and R is correct explanation of A.
Q. Assertion: When silver bromide is exposed to sunlight, it changes its colour from light yellow to grey
Reason: Silver bromide burns and becomes grey.
Ans: Assertion is true but reason is false.
Q. Assertion: If any food item containing oil or fat is left for a long time, it develops a bad taste and bad smell.
Reason: Food item undergoes decomposition to produce gases that result in bad smell.
Ans: Assertion is true but reason is false.
Q. What do you mean by exothermic reaction? Give one example
Ans: Exothermic reaction is a type of reaction in which heat is given out. In other words energy is produced. E.g
C + O -------------> CO2
C6H12O6 + 6O2 ------Ã 6CO2 + 6H2O
Q. What do you mean by Endothermic reaction? Give one example
Ans: Endothermic reaction is a type of reaction in which heat is absorbed. In other words energy is needed for reaction to take place. E.g
N2 + O2 -----------> 2NO
6CO2 + 6 H2O ----Ã C6H12O6 + O2
Q. What is balanced chemical equation? Why should chemical equations be balanced?
Ans: A balanced equation is a chemical equation which has equal number of atoms in reactants as well as products. The chemical equation needs to be balanced so that it follows the law of conservation of mass.
Q. Iron displaces copper from the copper sulphate solution to form iron sulphate. Write a balanced chemical equation for this reaction.Ans: Fe+CuSO4→Cu+FeSO4
Q. Reaction of Zinc with dilute Sulphuric acid is:
A. Displacement reaction as well as Redox reaction
B. Precipitation reaction as well as Redox reaction
C. A redox reaction as well as Double displacement reaction
D. A decomposition reaction as well as combination reaction.
Ans: A. Displacement reaction as well as Redox reaction
Q. Assertion: When we mix the solution of sodium sulphate and barium chloride, White precipitate is formed.
Reason: The white precipitate of barium sulphate and that is formed by the reaction of SO4 2- and Ba2+
(a) Both, A and R, are true and R is the correct explanation of A
(b) Both, A and R, are true but R is not the correct explanation of A
(c) If A is true but R is false
(d) If A is false but R is true
Ans: (a) Both, A and R, are true and R is the correct explanation of A
Q. Translate the following statements into chemical equations and balance them:
i. Hydrogen gas combines with nitrogen to form ammonia
Ans: 3H2 + N2 → 2NH3
ii. Barium chloride reacts with aluminium sulphate to give aluminium chloride and barium sulphate.
Ans: BaCl2 +Al2(SO4)3 → AlCl3 +BaSO4
iii. Potassium metal reacts with water to give potassium hydroxide and hydrogen gas
Ans: 2K +2H2O → 2KOH +n H2
Q. An element reacts with oxygen to give a compound with a high melting point. The compound is soluble in water. The element is likely to be:
a. Calcium b. Carbon c. Silicon d. Iron
Ans: Calcium
Hint: Calcium reacts with oxygen to form calcium oxide (CaO), Also called Quick Lime.
Q. A student performs an experiment to form aluminium chloride from aluminium and chlorine. Which of the following option gives the chemical equation of the reaction.
a) Al + Cl2 -> AlCI2
b) 2Al +3Cl, > 2AICl,
c) 2Al + CI2 -> 2AICI
d) 3Al +3Cl3 -> 3AICI3
Q. Which of the following reaction is used in black and white photography.
a) Combination reaction d) Oxidation reaction b) Decomposition reaction
c) Displacement reaction
Ans: b) Decomposition reaction
Q. CuO (s) + H2 (g) -> Cu (s) + H2O (l), In this
reaction:
a. Cu is an oxidising agent b. H20 is reducing agent
c. CuO is oxidizing agent d. Both CuO and H2 are oxidizing
agent
Ans: c. CuO is oxidizing agent
Q. 4 Na(s) + O2 (g)
-> 2 Na2O (s), In this reaction,
a. Sodium gets reduced
b. Sodium oxide gets reduced
c. Sodium oxide gets oxidized d. Sodium gets oxidized
Ans: d. Sodium gets oxidized
Q. An element reacts with oxygen to give a compound with
a high melting point. The compound is also soluble in water. The element is
likely to be:
a. Calcium b.
Carbon d. Silicon d. Iron
Ans: a. Calcium
Hint: Calcium reacts with oxygen to form Calcium oxide
(Quick Lime). It has high melting point and is soluble in water.
Q. Which of the following pairs will give displacement
reaction?
a. NaCl solution and copper metal b. MgCl2 solution and aluminium metal
c. FeSO4 solution and Silver metal d. AgNO3 solution and Copper metal
Ans: d. AgNO3 solution and Copper metal
Q. Fe2O3 + 2 Al -> Al2O3 + 2Fe, The reaction is an
example of:
a. Combination reaction
b. Displacement
Reaction
c. Double Displacement reaction d. Decomposition reaction
Ans: b. Displacement Reaction
Q. NaCl + AgNO3→ AgCl + NaNO3 The above reaction is a:
(A) Displacement reaction (B) Double displacement reaction (C) Combination reaction (D) None
Ans: (B) Double displacement reaction
