PUC Science 2nd PUC Class 12 - Karnataka Board PUC Important Questions for Chemistry

A reaction is second order in A and first order in B.

(i) Write the differential rate equation.

(ii) How is the rate affected on increasing the concentration of A three times?

(iii) How is the rate affected when the concentrations of both A and B are doubled?

For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction.

(b) Rate constant ‘k’ of a reaction varies with temperature ‘T’ according to the equation:

`logk=logA-E_a/2.303R(1/T)`

Where E_a is the activation energy. When a graph is plotted for `logk Vs. 1/T` a straight line with a slope of −4250 K is obtained. Calculate ‘E_a’ for the reaction.(R = 8.314 JK⁻¹ mol⁻¹)

 A first order reaction takes 40 minutes for 30% decomposition. Calculate t_1/2 for this reaction. (Given log 1.428 = 0.1548)

For a reaction: 

Rate = k

(i) Write the order and molecularity of this reaction.

(ii) Write the unit of k.

For the first order thermal decomposition reaction, the following data were obtained:

Time / sec               Totalpressure / atm

0                              0.30

300                          0.50

Calculate the rate constant

(Given: log 2 = 0.301, log3 = 0.4771, log 4 = 0.6021)

The rate constant of a first order reaction increases from 4 × 10⁻² to 8 × 10⁻² when the temperature changes from 27°C to 37°C. Calculate the energy of activation (Ea). (log 2 = 0.301, log 3 = 0.4771, log 4 = 0.6021)

A first order reaction takes 23.1 minutes for 50% completion. Calculate the time required for 75% completion of this reaction.

(log 2 = 0.301, log 3 = 0.4771, log 4 = 0.6021)

A reaction is second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is doubled?

A reaction is first order in A and second order in B. How is the rate affected on increasing the concentration of B three times?

A reaction is first order in A and second order in B. How is the rate affected when the concentrations of both A and B are doubled?

Which metal in the first transition series (3d series) exhibits + 1 oxidation state most frequently and why?

Which of the following cations are coloured in aqueous solutions and why ?

Sc³⁺, V³⁺, Ti⁴⁺, Mn²⁺ (At. Nos. Sc = 21, V = 23, Ti = 22, Mn = 25)

How would you account for the following? 

Transition metals exhibit variable oxidation states.

Complete the following chemical equations:

`(i) Cr_2O_7^(2-)+6Fe^(2+)+14H^+ ->`

`(ii) 2CrO_4^(2-)+2H^+ ->`

`(iii) 2MnO_4^-+5C_2O_4^(2-)+16H^+ ->`

Complete the following equations:

Complete the following equations: Cr₂O₇^2- + 14H⁺ + 6I →

The elements of 3d transition series are given as: Sc Ti V Cr Mn Fe Co

Answer the following: Write the element which shows maximum number of oxidation states. Give reason.

The elements of 3d transition series are given as: Sc Ti V Cr Mn Fe Co

Answer the following: Which element has the highest m.p?

The elements of 3d transition series are given as: Sc Ti V Cr Mn Fe Co

Answer the following: Which element shows only +3 oxidation state?