Chemistry

Chemical Kinetics

256 Questions

Chemical kinetics involves the study of chemical reaction rates and the factors affecting them, such as temperature and concentration. This topic covers rate laws, half-life, and zero, first, and second order reactions. It is a crucial part of the chemistry syllabus for various competitive examinations.

Reaction rate parametersFirst order kineticsZero and second orderHalf-life of reactionRate constant units

Chemical Kinetics Questions

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

In a certain reaction, 10% of the reactant decomposes in one hour, 20% in two hours, 30% in three hours and so on. Dimension of the velocity constant are:

  1. hour$^{-1}$
  2. mole litre$^{-1}$ hour$^{-1}$
  3. litre mol$^{-1}$ hour$^{-1}$
  4. mole sec$^{-1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For the zero-order reaction, the time taken for the decomposition of the reactant is independent of initial concentration which is the case here. 


The dimension of the velocity constant for the zero-order reaction is = mole litre$^{-1}$ hour$^{-1}$

Option B is correct.

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

When ethyl acetate was hydrolysed in presence of 0.1 N HCl, the rate constant was found to be $5.40\times 10^{-5}sec^{-1}$. But when 0.1 N $H _2SO _4$ was used for hydrolysis, the rate constant was found to be $6.25\times 10^{-5} sec^{-1}$. Thus, it may be concluded that:

  1. $H _2SO _4$ is stronger than HCl
  2. $H _2SO _4$ is weaker than HCl
  3. $H _2SO _4$ and HCl both have the same strength
  4. the data are not sufficient to compare the strength of $H _2SO _4$ and HCl
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Option (A) is correct.  $H _2SO _4$ is stronger than $HCl$.
Relative strength in favour of $H _2SO _4$
$=\frac {\text {rate constant of reaction catalysted by }H _2SO _4}{\text {rate constant of reaction catalysted by HCl}}$.

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

The rate constant (K) for the reaction, $2A+B\rightarrow$ Product was found to be $2.5\times 10^{-5}$ litre $mol^{-1} sec^{-1}$ after 15 sec, $2.60\times 10^{-5} litre\  mol^{-1} sec^{-1}$ after 30 sec and $2.55\times 10^{-5} litre \ mol^{-1}sec^{-1}$ after 50 sec. The order of reaction is:

  1. $2$
  2. $3$
  3. $0$
  4. $1$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

 The order of reaction is 2.


K does not change with time; thus its value remains unchanged during the reaction.

By seeing the equation, it can be said that reaction is a third order but the unit of K suggest it to be 2nd order.

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

For a gaseous reaction, $A\left( g \right) \longrightarrow $ Product, which one of the following is correct relation among $\dfrac { dP }{ dt } ,\dfrac { dn }{ dt }$ and $\dfrac { dc }{ dt } $?
($\dfrac { dP }{ dt } =$ Rate of reaction in $atm$ ${ sec }^{ -1 }$; $\dfrac { dc }{ dt } =$ Rate of reaction in molarity ${ sec }^{ -1 }$; $\dfrac { dn }{ dt } =$ Rate of reaction in $mol$ ${ sec }^{ -1 }$)

  1. $\dfrac { dc }{ dt } =\dfrac { dn }{ dt } =-\dfrac { dP }{ dt } $
  2. $-\dfrac { dc }{ dt } =-\dfrac { 1 }{ V } \dfrac { dn }{ dt } =-\dfrac {1}{RT}\dfrac{ dP }{ dt } $
  3. $\dfrac { dc }{ dt } =\dfrac { V }{ RT } \dfrac { dn }{ dt } =\dfrac { dP }{ dt } $

  4. None of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
$PV=nRT$
$\frac{dP}{dt}.V=RT.\frac{dn}{dt}$=> $\frac{1}{V}\frac{dn}{dt}=\frac{1}{RT}\frac{dP}{dt}$-(1)
Now, PV=nRT or $P=\frac{n}{V}RT$
Concentration $c=\frac{n}{V}$
P=cRT
$\frac{dP}{dt}=\frac{dc}{dt}.RT$=> \frac{dc}{dt}=\frac{1}{RT}\frac{dP}{dt}$
$-\frac{dc}{dt}=-\frac{1}{V}\frac{dn}{dt}=-\frac{1}{RT}\frac{dP}{dt}$
Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

The rate constant for the reaction is $2 10^{-4} s^{-1}.$ The reaction is :

  1. First order

  2. Second order

  3. Third order

  4. Zero order
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The unit of the rate constant is s^-1. This unit is characteristic of a first-order reaction, where the rate constant k has dimensions of time^-1.

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

For a second-order reaction of the type rate=$k[A]^2$ the plot of $\dfrac{1}{[A] _1}$ versus t is linear with a: 

  1. positive slope and zero intercept

  2. positive slope and non-zero intercept

  3. negative slope and zero intercept

  4. negative slope and non-zero intercept
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Given that for a second order reaction

$Rate= K[A]^2$

We know that rate of the reaction is decrease in the concentration of the reactant with respect to time.

$Rate= \cfrac {-d[A]}{dt}$
$\Rightarrow$ $\cfrac {-d[A]}{dt}=K[A]^2$
$\Rightarrow \cfrac {-d[A]}{[A]^2}=+Kdt$

Integrating both sides we have:-
$\Rightarrow -\int \cfrac {d[A]}{[A]^2}=+\int Kdt$
$\Rightarrow - \left[\cfrac {-1}{[A]}\right]=+Kt+C$
$\Rightarrow Kt+C= \cfrac {1}{[A]}$      $- (i)$

Now, from the equation $(i)$ we can see that graph of $\cfrac {1}{[A]}$ $V/s$ $t$ has a positive slope $K$ and non-zero intercept $C$.

Multiple choice evs eat when you need food poisoning and food preservation methods food spoilage, adulteration and preservation food spoilage and adulteration

Pasteurization is carried out at

  1. $30^o$C for $20$ minutes
  2. $40^o$C for $30$ minutes
  3. $30^o$C for $60$ minutes
  4. $62^o$C for $30$ minutes
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The 'batch' or 'vat' method of pasteurization involves heating milk to 62 degrees Celsius (or 145 degrees Fahrenheit) for 30 minutes.

Multiple choice nuclear reactions nuclear structure nuclei atomic nuclei physics

The unit of rate constant for a zero order reaction is:

  1. $s^{-1}$
  2. $mol L^{-1}s^{-1}$
  3. $L mol ^{-1}s^{-1}$
  4. $L^{2} mol ^{-2}s^{-1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation
For zero order reaction
Rate $=K[A]^0$
Rate $=K=\cfrac{d[A]}{dt}$
Unit of rate constant $=Unit\; of \; \cfrac{d[A]}{dt} \\=\cfrac{mol L^{-1}}{sec} \\=mol L^{-1} sec^{-1}$
Multiple choice

What does the word "rate" mean in reaction rate?

  1. How many reactants combine over a period of time

  2. How fast the temperature will increase or decrease
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In chemistry, the rate of a reaction refers to the speed at which reactants are converted into products over a specific interval of time.

Multiple choice

----- is depends on the initial concentration of reactants.

  1. rate constant

  2. order

  3. molecularity

  4. rate of a reaction
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The rate of a reaction is dependent on the concentration of reactants. Rate constants are independent of concentration, and order/molecularity are theoretical or empirical parameters.

Multiple choice

For a reaction 2A + B → 2C, with the rate equation: Rate = k[A]2[B]

  1. the order with respect to A is 1 and the order overall is 1

  2. the order with respect to A is 2 and the order overall is 2.

  3. the order with respect to A is 2 and the order overall is 3.

  4. the order with respect to B is 2 and the order overall is 2.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The order with respect to A is the exponent of [A], which is 2. The overall order is the sum of the exponents: 2 + 1 = 3.

Multiple choice

Which of the following statements for order of reaction is not correct?

  1. Order can be determined experimentally

  2. is = to the sum of power of concentration terms in differential rate law

  3. It is not affected with the stoichiometric coefficients of the reactants

  4. Order cannot be fractional
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The order of a reaction is an experimental value and can be zero, fractional, or an integer. Therefore, the statement that it cannot be fractional is incorrect.