Half life

Q.

The half-life period of a first order chemical reaction is 6.93 minutes.
The time required for 99% completion of reaction will be (log 2 = 0.301)

1. 230.3 min

2. 23.03 min

3. 46.06 min

4. 460.6 min

Q.

The reaction $2\mathrm{A}+{\mathrm{B}}_2\to 2\mathrm{AB}$ is an elementary reaction. For a certain quantity of reactants, if the volume of the reaction vessel is reduced by a factor of $3$, the rate of the reaction increases by a factor of $.......$

Q.

$O_2$ undergoes photochemical dissociation into one normal and one excited atoms. The excited atom has 1.967 eV more energy than normal. The dissociation of $O_2$ into two normal atoms requires 498 KJ mole-1. Then the maximum wavelength required for photochemical dissociation of $O_2$ is

1. 174nm

2. 7420A⁰

3. 1740A⁰

4. 742A⁰

Q.

Explain second-order reactions in details.

Q. For a first order reaction, the time taken for the initial concentration to become $1/4^{th}$, is 10 minutes. What will be the time required to reduce the initial concentration to 1/16 of the initial value?

1. 10 min
2. 20 min
3. 30 min
4. 40 min

Q. The half-life of a reaction is 50 minutes at a certain initial concentration. When the concentration is reduced to one-half, the half-life is found to be 25 minutes. The order of the reaction is:

1. Zero
2. One
3. Two
4. Three

Q. The graph between $\log T_{50}$ and $\log \left(\frac{1}{a}\right)$ (where $T_{50}$ and a are the half - life period and the concentration respectively) for a $n^{th}$ order reaction is of the type:

What is the value of n?

Q. If half-life period for a first order reaction is 2 min. The rate constant is

1. $0.5mi{n}^{-1}$
2. $1.386mi{n}^{-1}$
3. $0.3465mi{n}^{-1}$
4. $2mi{n}^{-1}$

Q. If $75\%$ of a first order reaction was completed in 90 minutes, $60\%$ of the same reaction would be completed in approximately:

1. $59.4min$
2. $22.1min$
3. $76.9min$
4. $32.8min$

Q. In a first order reaction, the reactant has a half-life period of ten minutes. What fraction of the substance will be left after an hour of the reaction has occured?

1. $\frac{1}{6}$ of the initial the concentration
2. $\frac{1}{64}$ of the initial the concentration
3. $\frac{1}{12}$ of the initial the concentration
4. $\frac{1}{32}$ of the initial the concentration

Q. The rate of a first order reaction is $0.69\times {10}^{-2}mi{n}^{-1}$and the initial concentration is 0.5 mol/L. The half life period is

1. 3000 s
2. 0.33 s
3. 50 s
4. 100 s

Q. The rate constant for a first order reaction whose half life is 480 sec is

1. $2.88\times {10}^{-2}{s}^{-1}$
2. $1.44\times {10}^{-3}{s}^{-1}$
3. $1.44s^{-1}$
4. $0.72\times {10}^{-3}{s}^{-1}$

Q. If 8 g of a radioactive isotope has a half life period of 10 hrs, the half-life period of 2g of the same substance is

1. 2.5 hrs
2. 5 hrs
3. 10 hrs
4. 40 hrs

Q. When initial concentration of the reactant is doubled, the half-life period of a zero order reaction

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1. is tripled
2. is halved
3. is doubled
4. remains unchanged

Q. The half life of a first order reaction is

1. Independent of the initial concentration of the reactant
2. Directly proportional to the initial concentration of the reactant
3. Inversely proportional to the initial concentration of the reactant
4. Directly proportional to the square of the initial concentration of the reactant

Q. If in the fermentation of sugar in an enzymatic solution which is initially 0.12 M the concentration of sugar is reduced to 0.06 M in 10 h and to 0.03 M in 20 h, hence order of the reaction is

1. \N
2. 1
3. 2
4. 3

Q. Identify the correct statement :

1. Half life of first order reaction is independent of temperature
2. For zero order reaction, half life depends on initial concentration of reactant
3. A reactant molecule having sufficient energy must get converted into product
4. First order reaction must be complex

Q. $nA\to B$ is a $1^{st}$ order reaction, whose concentration versus time curve is given below

If the half - life for the reaction is 24 minutes, then the value of n is

1. 1
2. 2
3. 3
4. 4

Q. The Ellingham diagram for different metals is given below.

The metal that can be reduced by most of the metals is:

1. A
2. D
3. F
4. C

Q.

why will the value of Kc not change if more amunt of reactant is added at the same temperature? wont the concentration of the reactants increase and hence the value of Kc should also increase?

Q. A first order reaction has a rate constant of ${10}^{-2}se{c}^{-1}$. How long will it take for a 20 g sample to become 5 g?

1. 138.6

Q. The rate constant for a first order reaction is $4.606\times {10}^{-3}{s}^{-1}$. The time required to reduce $2.0g$ of the reactant to $0.2g$ is :

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Q. ${}_2^{M}A\left(g\right){\to }_{Z-4}^{M-8}B\left(g\right)+\alpha -particles$
The radioactive disintegration follows first order kinetics. Starting with 1 mol of in a 1 litre closed flask at ${27}^{\circ }$C, pressure set up after two half-lives is approximately

1. 25 atm
2. 12 atm
3. 37 atm
4. 40 atm

Q. The ratio of the time taken for 99.9$\%$ reaction and half life of the reaction is

1. 100
2. 49.95
3. 10
4. 1000

Q. The correct difference between first and second order reactions is that

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1. the rate of a first-order reaction does depend on reactant concentrations; the rate of a second-order reaction does not depend on reactant concentrations
2. the rate of a first-order reaction does not depend on reactant concentrations; the rate of a second-order reaction does depend on reactant concentrations
3. a first-order reaction can be catalyzed; a second-order reaction cannot be catalyzed
4. the half-life of a first-order reaction does not depend on $\left[A_0\right]$; the half-life of a second-order reaction does depend on $\left[A_0\right]$

Q.

Under the same reaction conditions, initial concentration of 1.386 $mold{m}^{-3}$ of a substance becomes half in 40 s amd 20 s through first order and zero order kinetics respectively. Ratio $\left(\frac{k_1}{k_0}\right)$ of the rate constants for first order $\left(k_1\right)$ and zero order $\left(k_0\right)$ of the reaction is:

1. $0.5mo{l}^{-1}d{m}^3$

2. $1.0mold{m}^{-3}$

3. $1.5mold{m}^{-3}$

4. $2.0mo{l}^{-1}d{m}^3$

Q. For a reaction represented by $A\to B$, which of the following options give the value of order of the reaction.
$ROR=$ Rate of reaction
$C=$ Concentration of reactant $A$
$C_0=$ Concentration of reactant $A$ at $t=0$
$P=$ Concentration of product $B$
$t_{\frac{1}{2}}=$ Half life of $A$

1. $\frac{\log (ROR{)}_2-\log (ROR{)}_1}{\log C_2-\log C_1}$
2. $1+\left[\frac{\log t_{1/2}^{\prime }-\log t_{1/2}}{\log C_0-\log C_0^{\prime }}\right]$
3. Slope of $\ln ROR$ vs $\ln C$ graph
4. "$y-$ intercept" of $\ln ROR$ vs $\ln C$ graph

Q. Starting with one mole of a compound X, it is found that the reaction is $\frac{3}{4}$, complete in 1 min. What is the rate constant if the reaction follows first order?

1. $0.231s^{-1}$
2. $2.31s^{-1}$
3. $0.0231s^{-1}$
4. $2.31\times {10}^{-3}s-1$