HSC Science (Electronics) 12th Standard Board Exam - Maharashtra State Board Important Questions for Chemistry

The integrated rate equation for first order reaction is A → products

The rate constant for a first order reaction is 100 s^–1. The time required for completion of 50% of reaction is _______.

(A) 0.0693 milliseconds

(B) 0.693 milliseconds

(C) 6.93 milliseconds

(D) 69.3 milliseconds

The Arrhenius equation is_________________ .

(a)`k=Ae^(RT/E_a)`                                                    

(b)`A=ke^(-E_a/(RT))`

(c)`k=Ae^(-(RT)/E_a)`

(d)`k=Ae^(-E_a/(RT))`

Sucrose decomposes in acid solution to give glucose and fructose according to the first order rate law. The half life of the reaction is 3 hours. Calculate fraction of sucrose which will remain after 8 hours.

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)

What is pseudo first order reaction? Give one· example of it.

Consider the reaction

`3I_((aq))^-) +S_2O_8^(2-)->I_(3(aq))^-) + 2S_2O_4^(2-)`

At particular time t, `(d[SO_4^(2-)])/dt=2.2xx10^(-2)"M/s"`

What are the values of the following at the same time?

a. `-(d[I^-])/dt`

b. `-(d[S_2O_8^(2-)])/dt`

c. `-(d[I_3^-])/dt`

Derive a relation between ΔH and ΔU for a chemical reaction. Draw neat labelled diagram of calomel electrode. Resistance and conductivity of a cell containing 0.001 M KCI solution at 298K are 1500Ω and 1.46x10^-4 S.cm^-1 respectively.

Write molecularity of the following reaction:

2NO_(g)+O_2(g)→2NO_2(g)

For a reaction: 

Rate = k

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

(ii) Write the unit of k.

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)

What are fuel cells?

0.05 M NaOH solution offered a resistance of 31.6 Ω in a conductivity cell at 298 K. If the cell constant of the cell is 0.367 cm^-1, calculate the molar conductivity of NaOH solution.

In the Arrhenius equation for a first order reaction, the values of ‘A’ of ‘E_a’ are 4 × 10¹³ sec⁻¹ and 98.6 kJ mol⁻¹ respectively. At what temperature will its half life period be 10 minutes?

[R = 8.314 J K⁻¹ mol⁻¹]

The unit of rate constant for zero order reaction is _______.

(A) t^–1

(B) mol dm^–3 t^–1

(C) mol^–1 dm³ t^–1

(D) mol^–2 dm⁶ t^–1

Construct a labelled diagram for the following cell:

`Zn|Zn^(2+)(1M)||H^+(1M)|H_(2(g,1atm))|Pt`