Chemical Kinetics - ISC Class 12 Chemistry Questions with Answers, Page 3

Suppose 50 bacteria are placed in a flask containing nutrients, so that they can multiply. A study at $35^\circ\text{C}$ gave the following results:

Time (in minutes)	0	15	30	45	60
Number of bacteria	100	200	400	800	1600

Answer the following questions:

$20\%$ of a first order reaction is completed in five minutes. How much time will the $60\%$ reaction take to complete? Calculate the half-life period ($t_{1/2}$) for the above reaction.

Match the following:

A first order reaction is $50\%$ completed in $40\text{ minutes}$ at $300\text{ K}$ and in $20\text{ minutes}$ at $320\text{ K}$. Calculate the activation energy of the reaction. (Given: $\log 2 = 0\cdot3010$, $\log 4 = 0\cdot6021$, $R = 8\cdot314\text{ J K}^{-1}\text{mol}^{-1}$)

Fill in the blanks by choosing the appropriate word(s) from those given in the brackets: [two, Williamson’s synthesis, three, anisole, toluene, Friedel-Crafts alkylation, iodoform, sec-1, mol-1L sec-1, Lewis base, acetone, Lewis acid, chloroform, formaldehyde]

The rate constant for a first order reaction becomes six times when the temperature is increased from $350\text{ K}$ to $410\text{ K}$. Calculate activation energy ($E_a$) for the reaction.

Select and write the correct alternative from the choices given below: (i) The reaction of a primary amine with chloroform and ethanolic $\text{KOH}$ is called: (a) Carbylamine reaction (b) Kolbe’s reaction (c) Reimer-Tiemann reaction (d) Wurtz-Fittig reaction (ii) Which one of the following statements is TRUE for the Galvanic cell? (a) Electrons flow from copper electrode to zinc electrode. (b) Current flows from zinc electrode to copper electrode. (c) Cations move towards copper electrode. (d) Cations move towards zinc electrode. (iii) Which one of the following compounds is diamagnetic and colourless? (a) $\text{K}_2\text{Cr}_2\text{O}_7$ (b) $\text{ZnSO}_4$ (c) $\text{KMnO}_4$ (d) $\text{Cr}_2(\text{SO}_4)_3$ (iv) For a first order reaction, the half-life period ($t_{1/2}$) is: (a) proportional to the initial concentration. (b) inversely proportional to the initial concentration. (c) proportional to the square root of the initial concentration. (d) independent of the initial concentration.

(i) Assertion: If a solution contains both $\text{H}^+$ and $\text{Na}^+$ ions, the $\text{H}^+$ ions are reduced first at cathode. Reason: Cations with higher $E^\circ$ value are reduced first at cathode. (a) Both Assertion and Reason are true, and Reason is the correct explanation for Assertion. (b) Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion. (c) Assertion is true but Reason is false. (d) Assertion is false but Reason is true. (ii) Assertion: Addition of bromine water to 1-butene gives two optical isomers. Reason: The product formed contains two asymmetric carbon atoms. (a) Both Assertion and Reason are true, and Reason is the correct explanation for Assertion. (b) Both Assertion and Reason are true, but Reason is not the correct explanation for Assertion. (c) Assertion is true but Reason is false. (d) Assertion is false but Reason is true.

Fill in the blanks by choosing the appropriate word(s) from those given in the brackets: [stable, low, aldehyde, unstable, 6, 4, ethane, Clemmensen’s, 2, 3, carboxylic acid, high, propane, Rosenmund’s] (i) The primary alcohols are easily oxidised first into ____ and then into ____. (ii) The intermediate activated complex in a chemical reaction is highly ____ due to ____ energy. (iii) The coordination number and oxidation state of the complex $\text{K}_4[\text{Fe}(\text{CN})_6]$ are ____ and ____ respectively. (iv) Propanone on reaction with zinc amalgam in the presence of conc. $\text{HCl}$ gives ____ and the reaction is known as ____ reduction.

Select and write the correct alternative from the choices given below:

The rate of reaction becomes four times when the temperature changes from $293\text{ K}$ to $313\text{ K}$. Calculate the energy of activation ($E_a$) of the reaction assuming that it does not change with temperature. ($R = 8\cdot 314\text{ J K}^{-1}\text{mol}^{-1}$)

Answer the following:

Fill in the blanks by choosing the appropriate word(s) from those given in the brackets: (two, four, $\text{sec}^{-1}$, diamagnetic, acetaldehyde, $\text{mol}^{-1}\text{L }\text{sec}^{-1}$, paramagnetic, formaldehyde, acetone, ethanol)

Answer the following:

A first order reaction is $50\%$ completed in $30\text{ minutes}$ at $300\text{ K}$ and in $10\text{ minutes}$ at $320\text{ K}$. Calculate the activation energy of the reaction. ($R = 8\cdot314\text{ J K}^{-1}\text{mol}^{-1}$)

$25\%$ of a first order reaction is completed in $30\text{ minutes}$. Calculate the time taken in minutes for the reaction to go to $90\%$ completion.

For the reaction $\text{A} + \text{B} \rightarrow \text{C} + \text{D}$, the initial rate for different reactions and initial concentration of reactants are given below:

S. No.	Initial Conc. [A] ($\text{mole L}^{-1}$)	Initial Conc. [B] ($\text{mole L}^{-1}$)	Initial rate ($\text{mole L}^{-1}\text{ sec}^{-1}$)
1	1·0	1·0	$2 \times 10^{-3}$
2	2·0	1·0	$4 \times 10^{-3}$
3	4·0	1·0	$8 \times 10^{-3}$
4	1·0	2·0	$2 \times 10^{-3}$
5	1·0	4·0	$2 \times 10^{-3}$

Show that for a first order reaction the time required to complete $75\%$ of reaction is about $2$ times more than that required to complete $50\%$ of the reaction.

Identify the reaction order from each of the following rate constants: