The chapter Chemical Reactions and Equations is the most important in RBSE Class 10 Science. We have prepared 100 most important questions for class 10 science chemical reactions and equations.
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These important questions will be very useful and helpful for you. You should prepare notes yourself and practice them well.
Important Questions for Class 10 Science Chemical Reactions and Equations
1. Definethe following terms with a suitable example –
i. Combination reaction
ii. Decomposition reaction
iii. Displacement reaction
iv. Exothermic reaction
v. Endothermic reaction
vi. Oxidation
vii. Reduction
viii. Precipitation reaction
ix. Double displacement
x. Redox reaction
Answer
i. Combination reaction: – The chemical reaction in which two or more reactants (substances) react to produce on single product is called combination reaction.
Example – 2Mg +O2 →2MgO
ii. Decomposition reaction: – The chemical reaction in which one complex substance break down into two or more simpler substances, is called decomposition reaction.
Example – CaCO3 → CaO + CO2
iii. Displacement reaction: – The chemical reaction in which one more reactive element displaces or removes less reactive element from its compound, is called displacement reaction.
Example – Fe + CuSO4 →FeSO4 + Cu
iv. Exothermic reaction: – The chemical reaction in which heat is released during the formation of products, is called exothermic reaction.
Example – CH4 + 2O2 → CO2 + 2H2O +heat
v. Endothermic reaction: – The chemical reaction in which heat is absorbed from surroundings during the formation of products, is called endothermic reaction.
Example – N2 + O2 + heat → 2NO
vi. Oxidation reaction: – The chemical reaction in which a substance gains oxygen or loss hydrogen is called oxidation reaction.
Example – 2Mg + O2 → 2MgO
vii. Reduction reaction: – The chemical reaction
in which a substance gains hydrogen or loss oxygen is called reduction reaction.
Example – 2HgO →2Hg + O2
viii. Precipitation reaction: – The chemical reaction in which two aqueous solutions react to form an insoluble substance (precipitate) is called precipitation reaction.
Example – AgNO 3 + NaCl → AgCl↓ + NaNO3
ix. Double displacement reaction: – The chemical reaction in which two compounds exchange their ions and form new two compounds, is called double displacement reaction.
Example – AgNO 3 + NaCl → AgCl + NaNO3
x. Redox reaction: – The chemical
reaction in which oxidation and reduction take place simultaneously is called
redox reaction.
Example – Zn + CuSO4 →ZnSO4 + Cu
2. Identify the
following reactions and give their name –-
i. N2 + H2 → NH3
ii. H2O → H2 + O2
iii. CaCO3 → CaO + CO2
iv. AgNO 3 + NaCl → AgCl + NaNO3
Answer – The given reaction is –
i). Combination reaction – Two elements nitrogen and hydrogen combine to
form a new single substance ammonia.
ii). Decomposition reaction – A single compound water breaks down into
two simpler substance hydrogen and oxygen.
iii). Decomposition reaction – A single compound calcium carbonate
breaks down into two simpler substance calcium oxide and carbon dioxide.
iv). Double displacement reaction – Ion exchange between silver nitrate
and sodium chloride.
3. What happens when –(Give the chemical equation for the following reactions)
i. Calcium carbonate (CaCO3) is heated.
ii. Copper is burnt in air.
iii. Magnesium wire is burnt.
iv. Natural gas burns.
v. Quick lime reacts with water.
vi. Iron nails are put in the solution of copper sulphate.
vii. Lead nitrate is heated
viii. Silver chloride is kept in sunlight
ix. Silver bromide is kept in sunlight
x. Ferrous sulphate is heated
xi. Carbon dioxide is passed through lime water
Answer
i) Calcium carbonate decomposes into calcium oxide and carbon dioxide
CaCO3 → CaO + CO2
ii) Copper reacts with oxygen to form copper (II) oxide which is black in colour.
2 Cu + O2 →2CuO
iii) Burns with white flame and give white powder of magnesium oxide.
2Mg +O2 →2MgO
iv) Give carbon dioxide, water and heat.
CH4 + 2O2 → CO2 + 2H2O +heat
v) Quick lime give slaked lime (Ca(OH)2
CaO + H2O →Ca(OH)2
vi)
vi)Iron displaces copper form its salt solution and a brown layer is deposited on nails and pale green solution is formed
Fe + CuSO4 →FeSO4 + Cu
vii) Lead nitrate breaks down into lead oxide, brown nitrogen dioxide and oxygen
2Pb (NO3)2 → 2PbO + 4NO2 + O2
viii) Silver chloride decomposes into silver metal and chlorine gas.
2AgCl → 2Ag + Cl2
ix) Silver bromide decomposes into silver metal and bromine gas.
2AgBr → 2Ag + Br2
x) Ferrous sulphate decomposes into ferric oxide, sulphur trioxide and sulphur dioxide.
2FeSO4 → Fe2O3 + SO3 + SO2
xi) A milky white precipitate of calcium carbonate appears.
Ca(OH)2 +CO2 → CaCO3 + H2O
4. Name any two elements which are more reactive than copper.
Answer
Zinc and iron are more reactive than copper. They both displace copper from its solution.
5. Write the chemical formula of marble.
Answer
CaCO3
6. Give the equation for the reaction used in respiration?
Answer
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
7. Identify the substance that are oxidized and substances that are reduced in the
following reactions-
i. 4Na + O2 → 2N2O
ii. CuO + H2 → Cu + H2O
Answer
i). Substance oxidized – Na
Substance reduced – O2
ii). Substance oxidized – H2
Substance reduced – CuO
8. Write the chemical equations for the following statements–
i. Hydrogen gas combines with nitrogen to form ammonia.
ii. Barium chloride reacts with aluminium sulphate to give aluminium chloride and barium sulphate.
Answer
i). 3H2 + N2 → 2NH3
ii). BaCl2 + Al2(SO4)3 →AlCl3 + BaSO4
9. Define the following-
i. Word equation
ii. Skeletal equation
iii. Corrosion
iv. Rancidity
Answer
i). Word equation: – Chemical equation in which names of reactants and products are written is called word equation.
Example – Hydrogen + Oxygen → Water
ii). Skeletal equation: – The unbalanced chemical equation in which formula of reactants and products are written, is skeletal equation.
Example H2 + O2 → H2O
iii). Corrosion:- The process of eating away of the metal by the action of atmospheric reagents changing the metal into its compounds is called corrosion.
Example – Rusting of iron
iv). Rancidity: – When food items are kept unprotected for some time,
they give some unpleasant smell and taste or become rancid. This process is
called rancidity.
10. Why does the colour of copper sulphate solution change when an iron nail is dipped in it?
Answer
Iron is more reactive than copper. So, iron displaces copper form copper sulphate solution and forms ferrous sulphate solution which is of light green colour.
Fe + CuSO4 →FeSO4 + Cu
11. What information do we get from a balanced chemical equation?
Answer
A balanced chemical equation gives the following information
i. Reactants and products
ii. Physical states
iii. Number of molecules
12. In a container, solid calcium oxide was taken and water was added slowly to it.
a. State two observation made in the experiment.
b. Write the name and chemical formula of the product formed.
Answer
a). Two observations
i). The mixture becomes very hot so reaction is exothermic.
ii). A white slurry like solution is formed.
b). Calcium hydroxide, Ca (OH)2
13. Why should magnesium ribbon be cleaned before burning in air?
Answer
Magnesium ribbon is cleaned before burning to clean a layer of magnesium oxide that is formed when exposed to air.
14. Which type of reaction is the decomposition of vegetables?
Answer
It is a decomposition reaction and exothermic reaction. Complex organic compounds are broken down by the action of microorganisms.
15. How can you identify that a chemical reaction has taken place?
Answer
We can observe the following changes during a chemical reaction:
i. Change in colour
ii. Change in physical state
iii. Evolution of gas
iv. Formation of precipitate
v. Change in temperature
One or more changes can be taken place.
16. Why decomposition reactions are called the opposite of combination reactions? Give equations for these reactions.
Answer
|
Combination reaction |
Decomposition |
|
Two or more |
A single complex |
|
2Mg + O2 → 2MgO |
2H2O → 2H2 + O2 |
17. Write one equation each for decomposition where energy is supplied in the form of heat, light and electricity.
Answer
Decomposition reactions occurs when energy is supplied in the form of heat, light or elect city. Following are the examples of
1. Thermal decomposition :- The substance decomposes when heat is supplied.
heat
CaCO3 —–→ CaO + CO2
2. Photolytic decomposition: The substance decomposes when light is supplied.
sunlight
2AgCl ———→2Ag + Cl2
3. Electrolytic decomposition: – The substance decomposes when electricity is supplied.
electric current
2H2O ———–→2H2 + O2
18. In the refining of silver, the recovery of silver nitrate solution involved displacement by copper metal. Write the reaction involved.
Answer
2AgNO3(aq) +Cu(s)→ Cu(NO3)2(aq) + 2Ag(s)
Copper is more reactive than silver so it displaces silver from silver nitrate solution and copper nitrate and silver metal is obtained.
19. Why do apply paint on iron articles?
Answer
We apply paint on iron articles to prevent corrosion. Iron reacts with oxygen and moisture in the air to form rust (iron oxide).
Paint forms a protective layer on the surface of iron articles and this layer prevent iron come in contact with iron.
20. Oil and fat containing food items flushed with nitro gen, why?
Answer
Fats and oils get oxidised when they come in contact
with air, this oxidation causes rancidity which make the food spoil and foul taste
and smell.
So, food packets are filled with nitrogen because nitrogen is an inactive gas so it prevents oxidation.