31 Year NEET Previous Year Questions: Chemical Kinetics - NEET MCQ

For a first order reaction

When concentration A is doubled, rate is doubled. Hence order with respect to A is one.
When concentrations of both A and B are doubled, rate increases by 8 times hence order with respect to B is 2.
∴   rate = k [A]¹ [B]²
Total order = 1 + 2 = 3

E_a  >  ΔH

The value of rate constant can be increased by increasing the temperature.
∴ Correct choice : (b)

order of reaction may be zero, whole number or fractional.

For the reaction

For the reaction

For the reaction

Rate of disappearance of reactants = Rate of appearance of products

Rate = K(A)⁰ Unit of K = mol L^–1 sec^–1

According to statement given in the question, it is clear that r ∝ [A]² and r ∝ [B]
That means order of reaction with respect to B is 1 and w.r.t A is 2
Hence, Rate = k[A]²[B]¹

According to Arrhenius equation

= 34673 J mole^-1
= 34.7 J mole^-1

For a first order reaction, t_75% = 2 × t_50%

Rate = k[A]²[B]³ when concentrations of both A and B are doubled then rate = k[2A]²[2B]³ = 32 k[A]²[B]³
∴       rate will increase by a factor of 32.

From data 1 and 3, it is clear that keeping (B) const, When [A] is doubled, rate remains unaffected. Hence rate is independent of [A]. from 1 and 4, keeping [A] constant, when [B] is doubled, rate become 8 times. Hence [rate ∝ [ B]³].

 E_a(Forward) + ΔH = E_{a(back word)}
For Exothermic reaction, ΔH = –ve and
∴  activation energy of reactant is less than the energy of activation of products.

A catalyst affects equally both forward and backward reactions, therefore it does not affect equilibrium constant of reaction.

Given initial concentration (a) = 2.00 m; Time taken (t) = 200 min and final concentration (a – x)    = 0.15 m. For a first order reation rate constant,

Further

We know that the activation energy of chemical reaction is given by formula

where k₁ is the rate constant at temperature T₁ and k₂ is the rate constant at temperature T₂ and E_a is the activation energy.  Therefore activation energy of chemical reaction is determined by evaluating rate constant at two different temperatures.

t_1/2 = 4 s T = 16

where Å = initial concentration &  A = concentration left after time t

For reaction If it is zero order reaction r = k [A]⁰, i.e the rate remains same at any concentration of  'A'. i.e independent upon concentration of A.

∵ r = k[A]ⁿ
if n = 0
r = k[A]⁰ or  r = k thus for zero order reactions rate is equal to the rate constant.

A → B For a first order reaction given a = 0.8 mol,    (a – x) = 0.8 – 0.6 = 0.2

again a = 0.9,   a – x = 0.9 – 0.675 = 0.225

Hence t = 1 hour

In the given options  will not represent the reaction rate. It should not have –ve sign as it is product. since  show the rate of formation ofproduct C which will be positive.

For a first order reaction

when t = 60 and x = 60%

Now,

 =  45.31 min.

Rewriting the given data for the reaction

Actually this reaction is autocatalyzed and involves complex calculation for concentration terms.
We can look at the above results in a simple way to find the dependence of reaction rate (i.e. rate of disappearance of Br₂).
From data (1) and (2) in which concentration of CH₃COCH₃ and H⁺ remain unchanged and only the concentration of Br₂ is doubled, there is no change in rate of reaction. It means the rate of reaction is independent of concentration of Br₂.
Again from (2) and (3) in which (CH₃CO CH₃) and (Br₂) remain constant but H⁺ increases from 0.05 M to 0.10 i.e. doubled, the rate of reaction changes from 5.7×10^–5 to 1.2 × 10^–4 (or 12 × 10^–5), thus it also becomes almost doubled. It shows that rate of reaction is directly proportional to [H⁺].
From (3) and (4), the rate should have doubled due to increase in conc of [H⁺] from 0.10 M to 0.20 M but the rate has changed from 1.2× 10^–4 to 3.1×10^–4. This is due to change in concentration of CH₃ CO CH₃ from 0.30 M to 0.40 M. Thus the rate is directly proportional to [CH₃ COCH₃].
We now get rate = k [CH₃COCH₃]¹[Br₂]⁰[H⁺]1        
= k [CH₃COCH₃][H⁺].

Rate of disappearance of Br^–                
= rate of appearance of Br₂