1
MCQ (Single Correct Answer)

AIPMT 2011 Mains

The half-life of a substance in a certain enzyme-catalysed reaction is 138 s. The time required for the concentration of the substance to fall from 1.28 mg L$$-$$1 to 0.04 mg L$$-$$1 is
A
414 s
B
552 s
C
690 s
D
276 s

Explanation

We know, $$N = {N_0}{\left( {{1 \over 2}} \right)^n}$$

Give N0(original amount) = 1.28 mg L–1

N (amount of substance left after time T) = 0.04 mg L–1

$$ \therefore $$ $${{0.04} \over {1.28}} = {\left( {{1 \over 2}} \right)^n}$$

$$ \Rightarrow $$ $${1 \over {32}} = {\left( {{1 \over 2}} \right)^n}$$

$$ \Rightarrow $$ n = 5

$$ \therefore $$ Time required = 5 × t1/2 = 5 × 138 = 690 s
2
MCQ (Single Correct Answer)

AIPMT 2011 Mains

The unit of rate constant for a zero order reaction is
A
mol L$$-$$1 s$$-$$1
B
L mol$$-$$1 s$$-$$1
C
L2 mol$$-$$2 s$$-$$1
D
s$$-$$1

Explanation

Rate = K[A]0

Unit of k = mol L–1 sec–1
3
MCQ (Single Correct Answer)

AIPMT 2011 Mains

The rate of the reaction :   2N2O5 $$ \to $$ 4NO2 + O2
can be written in three ways.

$${{ - d\left[ {{N_2}{O_5}} \right]} \over {dt}} = k\left[ {{N_2}{O_5}} \right]$$

$${{d\left[ {N{O_2}} \right]} \over {dt}} = k'\left[ {{N_2}{O_5}} \right];\,\,$$ $${{d\left[ {{O_2}} \right]} \over {dt}} = k''\left[ {{N_2}{O_5}} \right]$$

The relationship between k and k' and between k and k'' are
A
$$k' = 2k ;  k'' = k$$
B
$$k' = 2k ;  k'' = k/2$$
C
$$k' = 2k ;  k'' = 2k$$
D
$$k' = k ;  k'' = k$$

Explanation

Rate of disappearance of reactants = Rate of appearance of products

$$ - {1 \over 2}$$$${{ - d\left[ {{N_2}{O_5}} \right]} \over {dt}}$$ = $${1 \over 4}$$$${{d\left[ {N{O_2}} \right]} \over {dt}}$$ = $${{d\left[ {{O_2}} \right]} \over {dt}}$$

$$ \Rightarrow $$ $${1 \over 2}$$$$k\left[ {{N_2}{O_5}} \right]$$ = $${1 \over 4}$$$$k'\left[ {{N_2}{O_5}} \right]$$ = $$k''\left[ {{N_2}{O_5}} \right]$$

$$ \Rightarrow $$ $${k \over 2} = {{k'} \over 4} = k''$$

$$ \Rightarrow $$ $$k' = 2k ;  k'' = k/2$$
4
MCQ (Single Correct Answer)

AIPMT 2011 Prelims

Which one of the following statements for the order of a reaction is incorrect?
A
Order can be determined only experimentally.
B
Order is not influenced by stoichiometric coefficient of the reactants.
C
Order of a reaction is sum of power to the concentration terms of reactants to express the rate of reaction.
D
Order of reaction is always whole number.

Explanation

Order of a reaction is not always whole number. It can be zero, or fractional also.

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