Half Life

Q. Half-life of a reaction is found to be inversely proportional to the cube of initial concentration. The order reaction is

1. 2
2. 3
3. 5
4. 4

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

Q.

The half - time period of a radioactive element is 140 days. After 650 days, one gram of the element will reduce to (J 1986)

1. $\frac{1}{8}g$

2. $\frac{1}{16}g$

3. $\frac{1}{2}g$

4. $\frac{1}{4}g$

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

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

Q. The half-life of a first order reaction is 24 hrs. If we start with 10 M initial concentration of the reactant then conc. after 96 hrs will be

1. 6.25 M
2. 0.125 M
3. 0.625 M
4. 1.25 M

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. The half life of a first order reaction is

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

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. $2.31\times {10}^{-3}s-1$

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

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

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

2. $1.5mold{m}^{-3}$

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

4. $1.0mold{m}^{-3}$

Q.

Half - lives of decomposition of $N{H}_3$ on the surface of a catalyst for different initial pressures are given as :
p(torr) 200 300 500
$t_{1.2\left(min\right)}$ 10 15 25
The order of the reaction is :

1. 2

2. 0

3. 1

4. 0.5

Q.

Under the same reaction conditions, the initial concentration of 1.386 mol $d{m}^{-3}$ of a substance becomes half in 40 s and 20 s through first order and zero order kinetics, respectively.

The ratio $(k_1/k_0$ of the rate constants for first order $\left(k_1\right)$ and zero order $\left(k_0\right)$of the reaction is

1. $0.5mol{}^{-1}d{m}^3$
2. $1.5mold{m}^{-3}$
3. $1.0mold{m}^{-3}$
4. $2.0mol{}^{-1}d{m}^3$

Q.

16 g of radioactive radon is kept in a container. How much radon will disintegrate in 19 days? Half life of radon is 3.8 days.

1. 5.5 g

2. 10.5 g

3. 15.5 g

4. 0.5 g