Chemical Kinetics MCQs for NEET — Chemistry Questions with Answers

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In a catalytic reaction involving the formation of ammonia by Haber's process N2+3H2 → 2NH3, the rate of appearance of NH3 was measured as 2.5 x 10-4 mol L-1S-1 The rate of disappearance of H2 will be

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Explanation

 N2+3H2 → 2NH3

     -1/3dH2/dt = -1/2dNH3/dt

     -dH2/dt = 1/2x3x2.5x10-4

     -dH2/dt = 3.75 x 10-4 mol L-1S-1

For a chemical reaction, A   products, the rate of reaction doubles when the concentration of A is increased by 4 times. The order of reaction is 

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Explanation

     Rate ∝ [A]x

     1/2 = 2 ∝ (4)x

        x = 1/2

Which of the following represents the expression for 3/4 th life of a first order reaction?

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Explanation

t3/4 = (2.303/K) log (a/(a/4)]

     t3/4 = (2.303/K)log4

For an endothermic reaction, where ΔH represents the enthalpy of the reaction in kJ/mol, the minimum value for the energy of activation will be

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Explanation

For endothermic reaction, energy of activation is always greater than H.

In the formation or sulphur trioxide by the contact process,

2SO2(g) + O2(g) 2SO3(g)

The rate of reaction is expressed as d(O2)/dt = 2.5x10-4 mol L-1sec-1. The rate disappearance of (SO2) will be

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Explanation

 2SO2 + O2 2SO3(g)

    -1/2dsO2/dt = -dO2/dt

    -dsO2/dt = 2x2.5x10-4 =5x10-4 mol L-1sec-1

A first order reaction complete 40% in 20 minutes. In how much time it is completed 90% of its original amount?

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Explanation

K = (2.303/t)log(a/a-x)

     when x = (40/100)a = 0.4a

     t = 20min

 K = (2.303/20)log(a/a-0.4a)

        =(2.303/20)log1/0.6

     K = 0.02554 min-1

     t = (2.303/0.02554)log(a/a-0.9a)

       =2.303/0.02554 log (1/0.1)

       =90.17 min

The dissociation of H2O2 is a first order reaction. The half life for '16 V H2O2 is 30 min, calculate the time at which the solution is 1V H2O2 ?

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Explanation

t = 2.303/(0.693/30)log 24/1

     or, t  = 30x4xlog2/0.3010

     or, t =120min.

How fast the reaction is at 25°C as compared to 0°C. If the activation energy is 65 KJ :-

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Explanation

The rate constant of a reaction depends on temperature according to the Arrhenius equation: k = A * e^(-Ea/RT). An increase in temperature from 0°C to 25°C raises the rate by a factor of e^(65000/8.314*(1/273 - 1/298)) ≈ 11 times, for an activation energy of 65 kJ/mol.

When temperature is increased from 27°C to 127°C, rate of reaction becomes doubled, then Ea will be?

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For a certain reaction, 10% of the reactant dissociates in 1 hour, 20% of the reactant dissociate in 2 hour, 30% of the reactant dissociates in 3 hour. Then the units of the rate constant is:-

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Explanation

The units of rate constant for a first-order reaction are mol L⁻¹ hr⁻¹ or s⁻¹. This is because the rate is proportional to the concentration of the reactant, which has units of mol L⁻¹, and the rate constant has units of time⁻¹, such as hr⁻¹ or s⁻¹.

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