Rate Constant

Trending Questions

Q. The decomposition of dimethyl ether leads to the formation of

C H_{4}, H_{2}

and CO and the reaction rate is given
By rate =

K [C H_{3} O C H_{3}]^{\frac{3}{2}}

The rate of reaction is followed by increase in pressure in a closed vessel and the rate can be expressed in terms of the partial pressure of dimethyl ether i.e, Rate =

K (p_{C} H_{3} O C H_{3})^{\frac{3}{2}}

If pressure is measured in bar and time in minutes, the units of rate constant are

$(b a r)^{\frac{3}{2}} m i n^{- 1}$
$(b a r)^{-} \frac{3}{2} m i n^{- 1}$
$(b a r)^{-} \frac{1}{2} m i n^{- 1}$
$(b a r)^{- 1} m i n^{- 1}$

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Q. An organic compound undergoes decomposition via first order kinetics. The time taken for its decomposition to

\frac{1}{8}

th and

\frac{1}{10}

th of its initial concentration are

\frac{t_{1}}{8}

and

\frac{t_{1}}{10}

respectively. What is the value of

\frac{[\frac{t_{1}}{8}]}{[\frac{t_{1}}{10}]} \times 10 ? ({log}_{10} 2 = 0.3)

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The gaseous reaction

A_{g} \to 2 B_{(} g) + C_{(} g)

obeys first order kinetics. The initial pressure is 90 mm and after 10 minutes it is 180 mm. The velocity constant ‘k’ of the reaction is:

$1.15 \times 10^{3} s^{- 1}$
$1.15 \times 10^{- 3} s^{- 1}$
$2.30 \times 10^{3} s^{- 1}$
$3.45 \times 10^{- 3} s^{- 1}$

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Q. The decomposition of hydrogen peroxide in an aqueous solution is a reaction of first order. It can be followed by titrating 10 mL portions of reaction mixture at various times from the beginning of reaction against a standard solution of

K M n O_{4}

. Volume of

K M n O_{4}

solution used in each case is proportional to the remaining concentration of

H_{2} O_{2}

. From the following data, calculate the rate constant of the reaction.

\begin{matrix} Time (in seconds) & 0 & 600 & 1200 K M n O_{4} sol. used (in mL) & 22.8 & 13.8 & 8.20 \end{matrix}

$k = 8.44 \times 10^{- 4} {sec}^{- 1}$
$k = 8.44 \times 10^{- 2} {sec}^{- 1}$
$k = 2.44 \times 10^{- 6} {sec}^{- 1}$
$k = 2.22 \times 10^{- 4} {sec}^{- 1}$

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Q. The pre-expontial factor in the Arrhenius equation of a first order reaction has the units -

$None of these$
$L {mol}^{- 1} s^{- 1}$
$mol L^{- 1} a^{- 1}$
$s^{- 1}$

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The following data pertains to reaction between A and B :
$\begin{matrix} S . N O . & [A] m o l L^{- 1} & m o l L^{- 1} & R a t e (m o l L^{- 1} t i m e^{- 1}) 1 & 1.0 \times 10^{- 2} & 2.0 \times 10^{- 2} & 2.0 \times 10^{4} 2 & 2.0 \times 10^{- 2} & 2.0 \times 10^{- 2} & 4.0 \times 10^{- 4} 3 & 2.0 \times 10^{- 2} & 4.0 \times 10^{- 2} & 8.0 \times 10^{- 4} \end{matrix}$
Which of the following inference(s) can be drawn from the above data ?

1. Rate constant of the reaction is $1.0 \times 10^{- 4}$

2. Rate law of the reaction is: rate $= k [A] [B]$

3. Rate of reaction increases four times on doubting the concentration of both the reactants.

Select the correct answer using the codes given below:

1, 2 and 3
1 and 2
2 and 3
3 only

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A reaction in which all reactants are in the same phase is called

elementary
bimolecular
homogeneous
heterogeneous

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For the reaction : $a A + b B \to$ Products, the rate law is given by Rate = $k [A]^{m} [B]^{n}$ . On making the concentration of A two-fold and halving that of B, the ratio of the new rate to the earlier rate of the reaction would be:

$n - 1$
$m + n$
$2^{- (m + n)}$
$2^{(m - n)}$

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On the top of a certain mountain where atmospheric pressure is 535 mm Hg, pure water shows a boiling point of 360 K and it takes $3 \times 10^{2}$ min to boil at the top of the mountain as against 3 min taken to boil an egg at 370 K. The ratio of rate constants $\frac{K_{370}}{K_{360}}$ is ?

$10$
$1$
$100$
$\frac{1}{10}$

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Q. If the rate constant for a first order reaction is k, the time (t) required for the completion of 99% of the reaction is given by:

t = 0.693/k
t = 6.909/k
t = 4.606/k
t = 2.303/k

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Q. What is the minimum concentration of

B a^{+ 2}

ions required in order to initiate the precipitation of

B a S O_{4}

from a solution containing

0.002 m o l L^{- 1}

S O_{4}^{- 2}

ions?
(Given

K_{s p}

for

B a S O_{4} = 1.4 \times 10^{- 10}

)

$1.7 \times 10^{- 7} M$
$2.7 \times 10^{- 7} M$
$7.0 \times 10^{- 8} M$
$7.0 \times 10^{- 10} M$

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Q. In an alkaline solution, the following equilibria exist.

S^{2 -} + S \to S_{2}^{2 -}

equilibrium constant

K_{1}

S_{2}^{2 -} + S \to S_{3}^{2 -}

equilibrium constant

K_{2}

K_{1}

and

K_{2}

have the values 12 and 11, respectively.

S_{3}^{2 -} \to S^{2 -} + 2 S

. What is equilibrium constant for the reaction?

$132$
$7.58 \times 10^{- 3}$
$1.09$
$0.198$

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\begin{matrix} Experiment No. & [A] (m o l d m^{- 3}) & [B] (m o l d m^{- 3}) & [C] (m o l d m^{- 3}) & Rate of the reaction (m o l d m^{- 3} s^{- 1}) 1 & 0.2 & 0.1 & 0.1 & 6.0 \times 10^{- 5} 2 & 0.2 & 0.2 & 0.1 & 6.0 \times 10^{- 5} 3 & 0.2 & 0.1 & 0.2 & 1.2 \times 10^{- 4} 4 & 0.3 & 0.1 & 0.1 & 9.0 \times 10^{- 5} \end{matrix}

The rate of the reaction for

[A] = 0.15 m o l d m^{- 3}, [B] = 0.25 m o l d m^{- 3} a n d [C] = 0.15 m o l d m^{- 3}

is found to be

Y \times 10^{- 5} m o l d m^{- 3} s^{- 1}

.The value of Y is

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Q. In a 1st order reaction A

\to

products, the concentration of the reactant decreases to 6.25

%

of its initial value in 80 minutes. What is (i) the rate constant and (ii) the rate of reaction, 100 minutes after the start, if the initial concentration is 0.2 mole/litre?

$3.465 \times 10^{- 2} m i n^{- 1}, 2.166 \times 10^{- 4} m o l . l i t r e^{- 1} m i n^{- 1}$
$3.465 \times 10^{- 3} m i n^{- 1}, 2.17 \times 10^{- 3} m o l . l i t r e^{- 1} m i n^{- 1}$
$2.166 \times 10^{- 3} m i n^{- 1}, 2.667 \times 10^{- 4} m o l . l i t r e^{- 1} m i n^{- 1}$
$2.17 \times 10^{- 2} m i n^{- 1}, 3.47 \times 10^{- 4} m o l . l i t r e^{- 1} m i n^{- 1}$

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A reaction : $A_{2} + B \to$ Products, involves the following mechanism :
$A_{2} ⇌ 2 A (f a s t)$ (A being the intermediate)
$A + B \to k_{2} (s l o w)$ .The rate law consistent to this mechanism is :

$r a t e = k [A_{2}] [B]$
$r a t e = k [A_{2}]^{2} [B]$
$r a t e = k [A_{2}]^{\frac{1}{2}} [B]$
$r a t e = k [A_{2}] [B]^{2}$

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Q. For the reaction

3 A (g) k \to B (g) + C (g)

, k is

10^{- 4} L m o l^{- 1} m i n^{- 1}

. If [A] = 0.5 M then the value of

\frac{- d [A]}{dt}

(in

M s^{- 1}

) is

$7.5 \times 10^{- 5}$
$3 \times 10^{- 4}$
$2.5 \times 10^{- 5}$
$1.25 \times 10^{- 6}$

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Q. For the first order decomposition reaction of

N_{2} O_{5}

, it is observed that

(i) N_{2} O_{5} (g) \to 2 N O_{2} (g) + \frac{1}{2} O_{2} (g); \frac{- d [N_{2} O_{5}]}{d t} = k [N_{2} O_{5}] (i i) 2 N_{2} O_{5} (g) \to 4 N O_{2} (g) + O_{2} (g); \frac{- d [N_{2} O_{5}]}{d t} = k^{'} [N_{2} O_{5}]

Which of the following is true?

$k = 2 k^{'}$
$k = \frac{k^{'}}{2}$
$k = k^{' \frac{1}{2}}$
$k = k^{'}$

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The chemical reaction $2 O_{3} \to 3 O_{2}$ involves two elementary steps :
$O_{3} f a s t - - \to O_{2} + O; O + O_{3} S l o w - -- \to 2 O_{2}$
The differential rate law expression will be :

$r a t e = k [O_{3}]^{2}$
$r a t e = k [O_{3}]^{2} [O_{2}]$
$r a t e = k [O_{3}]^{2} [O_{2}]^{- 1}$
$r a t e = k [O_{3}]^{2} [O_{2}]^{- 3}$

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Q. The decomposition of dimethyl ether leads to the formation of

C H_{4}, H_{2}

and CO and the reaction rate is given
By rate =

K [C H_{3} O C H_{3}]^{\frac{3}{2}}

The rate of reaction is followed by increase in pressure in a closed vessel and the rate can be expressed in terms of the partial pressure of dimethyl ether i.e, Rate =

K (p_{C} H_{3} O C H_{3})^{\frac{3}{2}}

If pressure is measured in bar and time in minutes, the units of rate constant are

$(b a r)^{\frac{3}{2}} m i n^{- 1}$
$(b a r)^{-} \frac{3}{2} m i n^{- 1}$
$(b a r)^{- 1} m i n^{- 1}$
$(b a r)^{-} \frac{1}{2} m i n^{- 1}$

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Q. For the first order decomposition reaction of

N_{2} O_{5}

, it is observed that

(i) N_{2} O_{5} (g) \to 2 N O_{2} (g) + \frac{1}{2} O_{2} (g); \frac{- d [N_{2} O_{5}]}{d t} = k [N_{2} O_{5}] (i i) 2 N_{2} O_{5} (g) \to 4 N O_{2} (g) + O_{2} (g); \frac{- d [N_{2} O_{5}]}{d t} = k^{'} [N_{2} O_{5}]

Which of the following is true?

$k = k^{'}$
$k = 2 k^{'}$
$k = \frac{k^{'}}{2}$
$k = k^{' \frac{1}{2}}$

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Q. The rate of a first order reaction is

1.8 \times 10^{- 3} m o l L^{- 1} m i n^{- 1},

when the initial concentration is 0.3 mol

L^{- 1}

. The rate constant in the units of second is

$10^{- 2} s^{- 1}$
$10^{- 4} s^{- 1}$
$6 \times 10^{- 2} s^{- 1}$
$6 \times 10^{2} s^{- 1}$

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Q. The pre-expontial factor in the Arrhenius equation of a first order reaction has the units -

$mol L^{- 1} a^{- 1}$
$L {mol}^{- 1} s^{- 1}$
$s^{- 1}$
$None of these$

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Q. A gaseous reaction A(g)

\leftrightarrow

2B(g) + C(g) is found to be of first order. If the reaction is started with p_A = 90 mm Hg, the total pressure after 10 min is found to be 180 mm Hg. The rate constant of the reaction is

$4.60 \times 10^{- 3} s^{- 1}$
$6.9 \times 10^{- 2} s^{- 1}$
$1.15 \times 10^{- 3} s^{- 1}$
$4.90 \times 10^{- 3} s^{- 1}$

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The rate constant for the forward and backward reactions of the hydrolysis of ester are

1.1 \times 10^{- 2}

and

1.5 \times 10^{- 3}

min^-1respectively. The equilibrium constant of the reaction is:

7.33
0.733
73.3
733

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1. Rate constant of the reaction is $1.0 \times 10^{- 4}$

2. Rate law of the reaction is: rate $= k [A] [B]$

3. Rate of reaction increases four times on doubting the concentration of both the reactants.

Select the correct answer using the codes given below:

1, 2 and 3
1 and 2
2 and 3
3 only

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Q. The unit of rate constant for a second order reaction is:

${mol}^{- 2} L^{2} s^{- 1}$
$s^{- 1}$
${mol L}^{- 1} s^{- 1}$
${L mol}^{- 1} s^{- 1}$

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Q. The time required for

100 %

completion of a zero order reaction is .
(a is the initial concentration and k is the rate constant)

$\frac{a}{k}$
$\frac{2 k}{a}$
$a k$

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Q. For the elementary reaction

M \to N

the rate of disappearence of M increases by a factor of 8 after doubling the concentration of M. The order of the reaction with respect to M is

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Q. It is possible to have a reaction where the rate of the reaction increases but the rate constant decreases.

True
False

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