Chemical Reactions and Equations — Class 10 Science PYQs

Directions : For question number 24, two statements are given, one labelled as Assertion (A) and the other is labelled as Reason (R). Select the correct answer to this question from the codes (A), (B), (C) and (D) as given below :
(A) Both, Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
(B) Both, Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
(C) Assertion (A) is true, but Reason (R) is false.
(D) Assertion (A) is false, but Reason (R) is true.
Assertion (A): Carbon shares its valence electrons with other atoms of carbon or with atoms of other elements.
Reason (R): The shared electrons belong to the outermost shells of both the atoms and lead to both atoms attaining the noble gas configuration.

In the following equation
$\text{x KI} + \ce{H2O2 -> I2} + \text{y KOH}$
x and y respectively are :

Answer the following :
(a) Why should chemical equations be balanced ?
(b) Name the oxidising and reducing agent in the following equation : $\ce{4Na + O2 -> 2Na2O}$

Translate the following statements into chemical equation and then balance them :
(a) Water is added to quicklime
(b) Burning of natural gas
(c) Thermal decomposition of ferrous sulphate

Which of the following are combination reactions ?
(i) $\ce{2KClO3 -> 2KCl + 3O2}$
(ii) $\ce{MgO + H2O -> Mg(OH)2}$
(iii) $\ce{4Al + 3O2 -> 2Al2O3}$
(iv) $\ce{Zn + FeSO4 -> ZnSO4 + Fe}$
Options:

The gases evolved on heating lead (II) nitrate crystals are :

When ferrous sulphate crystals are heated in a test tube, we observe that:

Which of the following are decomposition reactions ?
(i) $\ce{2KClO3 -> 2KCl + 3O2}$
(ii) $\ce{MgO + H2O -> Mg(OH)2}$
(iii) $\ce{2H2O -> H2 + O2}$
(iv) $\ce{Zn + CuSO4 -> ZnSO4 + Cu}$

Give reasons :
(i) Potato chips manufacturers fill the packet of chips with nitrogen gas.
(ii) Respiration is an exothermic reaction.
(iii) Silver chloride is stored in dark coloured bottles.

The volume ratio of hydrogen and oxygen gases liberated during electrolysis of water is

When lead nitrate is heated in a boiling tube, we observe :

Electrolysis of water is an example of :

(a) Name the substance oxidised and reduced in the following reaction : $\ce{ZnO + C -> Zn + CO}$
(b) Balance the following chemical reaction : $\ce{Pb(NO3)2 + KI -> PbI2 + KNO3}$
(c) Give one example each of electrolytic decomposition and decomposition by sunlight.

What happens when :
(a) silver chloride is kept in sunlight ?
(b) lead nitrate solution is added to potassium iodide solution?
(c) food materials containing fats and oils are left for a long time?

Answer the following :
(a) Write two observations when green coloured crystals of ferrous sulphate are heated in a boiling tube.
(b) Why brown coloured copper powder turns black on heating ?
(c) What happens when limestone is heated strongly ?

2 g of green coloured crystals of ferrous sulphate are heated in a dry boiling tube. Name the type of chemical reaction taking place. Write the balanced chemical equation for the reaction. Is this an exothermic or an endothermic reaction ?

Account for the following :
(a) White silver chloride turns grey when exposed to sunlight.
(b) Lead (II) nitrate on heating releases brown fumes.
(c) Bags of oil and fat containing food items are flushed with nitrogen gas.

What happens when
(i) lead (II) nitrate is heated ?
(ii) iron (II) sulphate is heated ?
(iii) silver chloride is exposed to sunlight ?
Write balanced chemical equations of the reactions involved in support of your answer.

What happens when
(i) Calcium carbonate is heated ?
(ii) Silver bromide is exposed to sunlight ?
(iii) Lead is added to copper (II) chloride solution ?
Write balanced chemical equations of the reactions involved in support of your answer.

Which of the following is an example of a displacement reaction ?

(i) $\ce{AgNO3 + NaCl -> NaNO3 + AgCl}$
(ii) $\ce{K2SO4 + BaCl2 -> BaSO4 + 2KCl}$
Which of the following options clearly describes both the reactions ?

What happens when
(i) potassium iodide solution is added to lead (II) nitrate solution ?
(ii) zinc is added to copper (II) chloride solution ?
(iii) hydrogen gas is passed over hot copper (II) oxide ?
Write balanced chemical equations of the reactions involved in support of your answer.

$\ce{C6H12O6(aq) + 6O2(g) -> 6CO2(g) + 6H2O(l)}$
The above reaction is an example of -

Define the following terms :
(a) Corrosion
(b) Rancidity
(c) Double displacement reaction

Define the following terms :
(i) Corrosion
(ii) Rancidity
(iii) Exothermic reaction

Assertion (A) : Reaction of quick lime with water is an exothermic reaction.
Reason (R) : A large amount of heat is evolved on the reaction of quick lime and water.

Which of the following is $\textit{not}$ an exothermic reaction ?