| Class | 10th |
| Subject | Science (NCERT) |
| Category | Important Questions |
Chemical Reaction and Equations Class 10 Science Chapter 1 Important Question Answer
Q1. What do you understand by endothermic reactions? Give one example.
Ans – Reactions in which energy is absorbed are known as endothermic reactions. Example. melting of ice cubes, melting of solid salts.
Q2. What do you mean by combination reactions? Give one example. Most Important
Ans – In this type of reaction two or more reactants are combined to form a single product.
Example- CaO + H2O → Ca(OH)2 + Heat
In the given example calcium oxide and water combine to form a single product, calcium hydroxide.
Q3. What do you mean by displacement reaction? Give one example. Most Important
Ans – It is a type of reaction in which a more active element displaces less active element.
Example – Zn + CuSO4 → ZnSO4 + Cu. In this example zinc displaces copper from copper sulphate solution as zinc is more reactive than copper.
Q4. What do you mean by decomposition reactions? Give one example (chemical equation).
Ans – In this type of reaction single reactant is breaks down to two or more simpler products.
Example – CaCO3 → CaO + CO2. In this given example calcium carbonate is decomposed to calcium oxide and carbon dioxide on heating.
Q5. What do you mean by Precipitation reaction? Give one example.
Ans – Any reaction that produces a precipitate can be called a precipitation reaction.
Example – Na2SO4 (aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)
The white precipitate of BaSO4 is formed by the reaction of 
and Ba2+
Q6. Write the balanced chemical equation for the following reaction:
Barium chloride + Aluminium sulphate → Barium sulphate + Aluminium chloride
Ans – 3BaCl2 + Al2(SO4)3 → 3BaSO4+2AlCl3
Q7. Write one equation each for decomposition reactions where energy is supplied in the form of heat and light.
Ans – Decomposition of Calcium Carbonate (CaCO3) when heat is supplied is as :
CaCO3 (s) → CaO(s) + CO2 (g)
Q8. Why does the colour of copper sulphate solution change when an iron nail is dipped in it? Give chemical equation for it.
Ans – Because when an iron nail in a copper sulphate solution is dipped, iron replaces copper from copper sulphate solution forming iron sulphate.
The colour of blue coloured copper sulphate solution changes into green.
Chemical reaction : Fe(s) + CuSO4 (aq) → FeSO4 (aq) + Cu(s)
Q9. Write the balanced chemical equation for the following reaction:
Aluminium + Copper Chloride → Aluminium Chloride + Copper
Ans – 2Al + 3CuCl2 → 2AlCl3 + 3Cu
Q10. Fat and oil containing foods are packed with which gas and why?
Ans – Fat and oil containing foods are packed with nitrogen gas to prevent them from oxidation.
Q11. Why should Mg ribbon be cleaned before burning in air ?
Ans – Magnesium is a reactive metal and combines with oxygen in air to form layer of magnesium oxide on its surface. This oxide protects magnesium from burning. Therefore, it is should be cleaned with sandpaper before burning in air.
Q12. What do you mean by double displacement reactions? Give one example (chemical equation).
Ans – In this type of reaction two elements displaces each other from their respective solutions.
Example – Na2SO4 + BaCl2 → Ba SO4 + 2NaCl
Q13. What is rancidity?
Ans – It is the process in which fat/oil containing food materials become rancid and their taste and smell changes in the presence of oxygen. This happens because these items gets oxidised.
Q14. Why is respiration considered as exothermic reaction? Explain.
Ans – Respiration is considered as exothermic reaction because heat is produced during the process of respiration. During respiration, carbon dioxide in food is broken down into glucose during this process. This glucose reacts with oxygen in our cells, releasing a large amount of energy.
Q15. What is a balanced chemical equation? Why should chemical equations be balanced?
Ans – In a balanced chemical equations the number of atoms in each side either in reactant or product must be equal. This equality of atoms in chemical equations is called balanced chemical equations.
The chemical equation needs to be balanced so that it follows the law of conservation of mass.
Q16. Which reactant is Oxidised in the following chemical reaction?
CuO + H2 → Cu + H2O
Ans – Hydrogen is oxidised.
Q17. Which of the following reactant is reduced in chemical reaction?
Cuo + H2 → Cu + H2O
Ans – Copper oxide is reduced as it loses oxygen.
Q18. What is the colour of Ferrous sulphate crystals? How does this colour change after heating ?
Ans – The colour of Ferrous sulphate crystals is green. After heating this colour change to white. This is because the water in the crystals evaporates and anhydrous ferrous sulphate is produced, changing the colour of the crystals from green to white.
Q19. What is redox reaction ? Give an example.
Ans – A reaction in which one reactant gets oxidised is called oxidation reaction and a reaction in which one reactant gets reduced is called Reduction Reaction. When both of them combined is called Oxidation-Reduction reactions or redox reactions.
Example – CuO + H2 → Cu + H2O . In this example copper oxide is losing oxygen and is reduced. The hydrogen is gaining oxygen and is being oxidised.
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