Science (English Medium) Class 12 - CBSE Important Questions for Chemistry

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?

What is the effect of adding a catalyst on Activation energy (E_a)

A first order reaction takes 20 minutes for 25% decomposition. Calculate the time when 75% of the reaction will be completed.

(Given : log = 2 = 0·3010, log 3 = 0·4771, log 4 = 0·6021)

Define the following terms: Rate constant

A first order reaction takes 10 minutes for 25% decomposition. Calculate t_1/2 for the reaction.

(Given : log 2 = 0.3010, log 3 = 0.4771, log 4 = 0.6021)

Write two differences between 'order of reaction' and 'molecularity of reaction'.

Write the principle behind the following methods of refining:

Hydraulic washing

Define the following terms:

Half-life period of reaction (t_1/2).

Explain the following terms :

Rate constant (k)

Explain the following terms :

Half life period of a reaction (t_1/2)

Define order of reaction. How does order of a reaction differ from molecularity for a complex reaction? 

 A first order reaction is 50% complete in 25 minutes. Calculate the time for 80% completion of the reaction.

The decomposition of a hydrocarbon has value of rate constant as 2.5×10⁴s^-1 At 27° what temperature would rate constant be 7.5×10⁴ × ³ s^-1if energy of activation is  19.147 × 10³ J mol^-1 ?