Question

Analyse the given graph, drawn between concentration of reactant vs. time.
(A)Predict the order of reaction.
(B)Theoretically, can the concentration of the reactant reduce to zero after infinite time?Explain.​

Answer 1

Answer:

I think Second Order

T1/2 is 10 min

Time 2 times karne se Concentration aadhi ho gai

Time =

$time \infty$

Answer 2

Answer: (A) The reaction is First order

(B) Yes , Theoretically, the concentration of the reactant can reduce to zero after infinite time.

Explanation:

From the graph,

(A)

we can see with increase in time the concentration of reactant decreases exponentially. So we can say the reaction must be first order.

on the other hand

from the graph, we get

at, t = 10 , C = 0.8

   t = 20 , C = 0.4                                          [ here C = concentration at time t

   t = 30 , C = 0.2                                                       t = time]

using first order reaction,

$[A]=[A]_{0} e^{-kt}$                                         $[A]_{0}$ = Initial concentration of reactant

⇒$[A]_{0}=[A]e^{kt}$                                       [A] = Concentration at time t = C

now if t = 10 , C = 0.8

$[A]_{0}=0.8e^{10k}$ .......... (i)

if t = 20, C = 0.4

$[A]_{0}= 0.4e^{20k}$ .......... (ii)

it t = 30 , C = 0.2

$[A]_{0}=0.2e^{30k}$ .............(iii)

now comparing equation (i) and (ii)

$0.8e^{10k}=0.4e^{20k}\\or, \frac{0.8}{0.4}=e^{20k-10k}\\ or, 2=e^{10k}$

using ln at both side

ln (2) = ln ($e^{10k}$)

or, 0.693 = 10k

or, k = 0.0693 $s^{-1}$

now comparing equation (ii) and (iii)

$0.4e^{20k}=0.2e^{30k}\\or, \frac{0.4}{0.2}=e^{30k-20k}\\ or, 2=e^{10k}$

using ln at both side

ln (2) = ln ($e^{10k}$)

or, 0.693 = 10k

or, k = 0.0693 $s^{-1}$

both case we get same value of k, and it satisfy first order equation.

So the reaction must be first order.

(B)

For the first order reaction

$[A]=[A]_{0} e^{-kt}$

if the reaction complete then [A] = 0, but $[A]_{0}\neq 0$

So $e^{-kt}=0$

⇒t = ∞                        [ since k is rate constant]

so we can say that,

Theoretically, the concentration of the reactant can reduce to zero after infinite time