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 pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

The value of rate constant of a pseudo first order reaction ________.

  1. depends on the concentration of reactants present in small amount

  2. depends on the concentration of reactants present in excess

  3. is independent of the concentration of reactants

  4. depends only on temperature
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pseudo first-order reaction is not the first-order reaction by nature. It is made the first order by adding something in excess.so, the rate constant depends on the concentration of reactants present in excess.

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

Which of the following is/are correct?

  1. Acid hydrolysis of an ester follows pseudo first order kinetics

  2. Inversion of cane sugar follows pseudo first order kinetics
  3. Decomposition of varous gases on the surface of metallic catalysts, such as decomposition of $HI$ on gold surface also exhibits zero roder kinetics

  4. Radioactivity follows first order kinetics
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
Explanation

 Pseudo first order reaction is a reaction in which concentration of one of the species dominates over the other. Hence the reaction follows the first order kinetics.

Options A, B and C all are the examples of pseudo first order reaction.
Radioactive decay follows first order reaction.

$\mathbf {Hence\ all\ the\ options\ are\ correct.}$

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

Rate law for the following reaction; $Ester+H^+\rightleftharpoons Acids+ Alcohol$; is $\frac {dx}{dt}=k [ester]^1 [H^+]^0$. What would be the effect on the rate if concentration of $H^+$ ion is doubled?

  1. Same

  2. Doubled

  3. Half

  4. Data insufficient
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As reaction does not depend on the concentration of $H^+$, therefore, rate will be the same.

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

A first-order reaction which is $30\%$ complete in $30$ minutes has a half-life period of:

  1. $24.2\ min$
  2. $58.2\ min$
  3. $102.2\ min$
  4. $120.2\ min$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

It is a 1st order reaction


$k = \dfrac{2.303}{t} log \dfrac{a}{a-x}$

but $k=\dfrac{0.693}{t _{\frac{1}{2}}}$

$\dfrac{0.693}{{t} _{1/2}} = \dfrac{2.303}{30} log \dfrac{100}{70}$

${t} _{1/2} = 58.2 min$

Hence, the correct option is $B$

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

The rate of reaction, $A+B\longrightarrow $ Products, is given by the equation, $r=k\left[ A \right] \left[ B \right] $. If $B$ is taken in large excess, the order of reaction would be:

  1. $2$
  2. $1$
  3. $0$

  4. Unpredictable
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

If $B$ is in excess then $A$ is limiting reagent thus

$ \vartheta =k[A]$
$ \therefore$ order$=1.$

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

The rate of a first order reaction is $0.04$ mole ${ \ell  }^{ -1 }{ S }^{ -1 }$ at $10$ seconds and $0.03$ mol ${ \ell  }^{ -1 }{ S }^{ -1 }$ at $20$ seconds after initiation of the reaction. The half-life period of the reaction is:

  1. $48.1$ s
  2. $24.1$ s
  3. $34.1$ s
  4. $44.1$ s
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
$\vartheta =kA\rightarrow $first order

$\vartheta =kA _{0}e^{-kt}$

$\vartheta =\vartheta _{0}e^{-kt}\rightarrow $first order wrt $\vartheta$
so,

$\vartheta _{10}=0.04=\vartheta _{0}e^{-10k}\rightarrow (1)$

$\vartheta _{30}=0.03=\vartheta _{0}e^{-30k}\rightarrow (2)$

now using (1)/(2)
$+l _{n}(1.33)=20k$

$k=0.0144$

now,$t _{\frac{1}{2}}=\frac{0.693}{k}$

$=48.125$

$\cong 50$ seconds
Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

In a pseudo first order acid catalysed hydrolysis of ester in water the following results were obtained:
t/s             0      30       60        90
[ester]/M    0.55 0.31   0.17       0.085
Which of the following is/are correct for the given reaction?

  1. The average rate of reaction between time interval 30 to 60 seconds is $4.67\times 10^{-3} mol L^{-1} s^{-1}$

  2. Order of reaction is 2.
  3. Pseudo first order rate constant for the acid catalysed hydrolysis of ester is $1.92\times 10^{-2}s^{-1}$

  4. All are correct.
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

$rate _{avg}=0.14/30=4.67\times 10^{-3}$
$\therefore k=1.92\times 10^{-2}$

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

An optically active compound A upon acid catalysed hydrolysis yield two optically active compound B and C by pseudo first order kinetics. The observed rotation of the mixture after 20 min was $ 20^{\circ}$ while after completion of the reaction it was $-20 ^{\circ} .$ If optical rotation per mole of A,B &C are 60$ ^{\circ} ,40$ $^{\circ}$& $-80 ^{\circ} . $Calculate half life of the reaction.

  1. 20 min

  2. 24 min

  3. 28 min

  4. 32 min
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As after completion of the reaction rotation is $-20 ^{\circ} $
So according to first order reaction
$k = 2.303log(r _0 - r _{\infty })/(r _t - r _{\infty })/20 = 2.303log(80/40)/20$
$t _{1/2} = 0.693/k = 20 min$

Multiple choice pseudo first order reaction order of reactions chemical kinetics electrochemistry and chemical kinetics chemistry

Consider the reaction represented by the equation represented by the equation
$CH _3Cl(g)\, +\, H _2O(g)\, \rightarrow\, CH _3OH(g)\, +\, HCl(g)$
These kinetic data were obtained for the given reaction concentrations

Initial conc (M) Initial conc (M) Initial rate of disappearance of
$[CH _3Cl]$ $[H _2O]$ $CH _3Cl\, (M\, s^{-1}$
0.2 0.2 1
0.4 0.2 2
0.4 0.4 8

If $H _2O$ is taken in large excess, the order of the reaction will be:

  1. 1

  2. 2

  3. 3

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Comparing the rate law, the order w.r.t. $H _2O\, =\, 2$.
w.r.t. $[CH _3Cl]\, =\, 1$
$\therefore \, r\, =\, [CH _3Cl]\, [H _2O]^2$
Overall order = 1 + 2 = 3
If $H _2O$ is in excess, the order of the reaction will be 1.

Multiple choice chemistry chemical equilibrium relationship between equilibrium constant, reaction quotient and gibbs energy law of mass action chemical equilibrium and acids-bases

Which of the following is true about the reaction quotient?

  1. It relates the ratio of the concentrations of products to reactants once the reaction has reached chemical equilibrium.

  2. It is always equal to the equilibrium constant.

  3. It can never be equal to the equilibrium constant.

  4. It relates the concentrations of products to reactants at any point in time.

  5. None of these answers are correct
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The reaction quotient relates the concentrations of products to reactants at any point in time.
When equilibrium is attained, the reaction quotient is equal to the equilibrium constant.

Multiple choice chemistry introduction to analytical chemistry interpreting a balanced chemical reaction percentage yield stoichiometric calculations

What equation is used to calculate percent yield?
Note: $E=$ experimental; $T=$ theoretical

  1. $\cfrac{E}{T}\times 100$
  2. $\cfrac{(E-T)}{T}\times 100$
  3. $\cfrac{T}{E}\times 100$
  4. $\cfrac{(T-E)}{T}\times 100$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The calculated or expected amount of product is called theoretical yield. The amount of product actually produced is called actual yield.

When we divide actual yield by the theoretical yield and then multiplied by 100 to get the percentage yield of reaction.
$\Rightarrow \dfrac{E}{T} \times 100 = \% $ Yield

Multiple choice chemistry introduction to analytical chemistry interpreting a balanced chemical reaction percentage yield stoichiometric calculations

A reaction is known to have a percent yield of $80$%. It the actual yield is $25$ grams, what was the expected yield?

  1. $3.2\ grams$
  2. $19\ grams$
  3. $31.25\ grams$
  4. $190\ grams$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Percent yield is the ratio of actual yield to the expected yield of compound.

$\%$ Yield $= \dfrac{\text{Actual Yield}}{\text{Expected Yield}} \times 100$
$\Rightarrow 80 = \dfrac{25}{\text{Expected Yield}} \times 100$
$\Rightarrow$ Expected Yield $= \dfrac{25}{80} \times 100 = \dfrac{250}{8} = 31.259\space g$

Multiple choice chemistry how far? how fast? collision theory collision theory of chemical reactions rate of chemical reaction

A chemical reaction occurs as a result of collisions between reacting molecules. Therefore, the reaction rate is given by:

  1. total number of collision occuring in a unit volume per second

  2. fraction of molecules which possess energy less than the threshold energy

  3. total number of effective collisions

  4. none of the above
Reveal answer Fill a bubble to check yourself
A,C Correct answer
Explanation

According to collision theory, the reaction occurs when molecules collide with each other. The rate is given by:

Rate=${ Z } _{ AB }\times f$

Where $Z _{AB}$=collision frequency of reactants $A$ & $B$.

i.e. total number of collisions occurring in a unit volume per second. &

$f$=fraction of effective collisions.

So, the rate depends on both (A) & (C)