Science (English Medium) Class 12 - CBSE Question Bank Solutions for Chemistry

For which type of reactions, order and molecularity have the same value?

In a reaction if the concentration of reactant A is tripled, the rate of reaction becomes twenty seven times. What is the order of the reaction?

For a general reaction A → B, plot of concentration of A vs time is given in figure. Answer the following question on the basis of this graph.

(i) What is the order of the reaction?

(ii) What is the slope of the curve?

(iii) What are the units of rate constant?

Why is the probability of reaction with molecularity higher than three very rare?

Why does the rate of any reaction generally decreases during the course of the reaction?

Why can’t molecularity of any reaction be equal to zero?

Why molecularity is applicable only for elementary reactions and order is applicable for elementary as well as complex reactions?

Why can we not determine the order of a reaction by taking into consideration the balanced chemical equation?

Match the graph given in Column I with the order of reaction given in Column II. More than one item in Column I may link to the same item of Column II.

	Column I	Column II
(i)
(ii)		(a) 1st order
(iii)		(b) Zero-order
(iv)

Assertion: Order of the reaction can be zero or fractional.

Reason: We cannot determine order from balanced chemical equation.

Assertion: Order and molecularity are same.

Reason: Order is determined experimentally and molecularity is the sum of the stoichiometric coefficient of rate determining elementary step.

Assertion: The enthalpy of reaction remains constant in the presence of a catalyst.

Reason: A catalyst participating in the reaction, forms different activated complex and lowers down the activation energy but the difference in energy of reactant and product remains the same.

Assertion: Rate constants determined from Arrhenius equation are fairly accurate for simple as well as complex molecules.

Reason: Reactant molecules undergo chemical change irrespective of their orientation during collision.

Why does the white precipitate of silver halide become coloured in the presence of dye eosin.

When copper ore is mixed with silica, in a reverberatory furnace copper matte is produced. The copper matte contains ______.

Which of the following options are correct?

(i) Cast iron is obtained by remelting pig iron with scrap iron and coke using hot air blast.

(ii) In extraction of silver, silver is extracted as cationic complex.

(iii) Nickel is purified by zone refining.

(iv) Zr and Ti are purified by van Arkel method.

In the extraction of aluminium by Hall-Heroult process, purified \[\ce{Al2O3}\] is mixed with \[\ce{CaF2}\] to:

(i) lower the melting point of \[\ce{Al2O3}\].

(ii) increase the conductivity of molten mixture.

(iii) reduce \[\ce{Al^{3+}}\] into \[\ce{Al(s)}\].

(iv) acts as catalyst.

Which of the following reactions occur during calcination?

(i) \[\ce{CaCo3 -> CaO + CO2}\]

(ii) \[\ce{2FeS2 + 11/2 O2 -> Fe2O3 + 4SO2}\] 

(iii) \[\ce{Al2O3. {x}H2O -> Al2O3 + {x}H2O}\]

(iv)  \[\ce{ZnS + 3/2 O2 -> ZnO + SO2}\]

The main reactions occurring in blast furnace during extraction of iron from haematite are:

(i) \[\ce{Fe2O3 + 3CO -> 2Fe + 3CO2}\]

(ii) \[\ce{FeO + SiO2 -> FeSiO3}\] 

(iii) \[\ce{Fe2O3 + 3C -> 2Fe + 3CO}\]

(iv) \[\ce{CaO + SiO2 -> CaSiO3}\]

Although carbon and hydrogen are better reducing agents but they are not used to reduce metallic oxides at high temperatures. Why?