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Chemical Kinetics Chemistry - Chemical Kinetics

Rajasthan Board (RBSE) - STD 12 Science - Chemistry (Rajasthan - English Medium). 200 questions in this chapter.

Question types

Chemical Kinetics question types

200 questions across 6 question groups — pick any mix to generate a Chemistry paper with step-by-step answer keys.

200
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6
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5
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Sample Questions

Chemical Kinetics questions

One sample from each question group in this chapter. Select any group above to see the full set with answer keys.

Q 1M.C.Q (1 Marks)1 Mark
Which of the following is not correct reason for the substantially lower rate of reaction than the collision frequency?
  • A
    All the collisions do not attain threshold energy level.
  • ✓
    The activated complex formed is short lived.
  • C
    All the collisions do not have proper orientation.
  • D
    Effective collision are lesser in number than all collisions.

Answer: B.

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Q 2M.C.Q (1 Marks)1 Mark
In general, the rate of a reaction can be increased by all the factors except:
  • A
    Increasing the temperature.
  • B
    Increasing the concentration of reactants.
  • ✓
    Increasing the activation energy.
  • D
    Using a catalyst.

Answer: C.

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Q 3M.C.Q (1 Marks)1 Mark
If hydrogen and oxygen are mixed and kept in the same vessel at room temperature, the reaction does not take place to form water because:
  • ✓
    Activation energy for the reaction is very high at room temperature.
  • B
    Molecules have no proper orientation to react to form water.
  • C
    The frequency of collisions is not high enough for the reaction to take place.
  • D
    No catalyst is present in the reaction mixture.

Answer: A.

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Q 4M.C.Q (1 Marks)1 Mark
For a first $-$ order reaction, the concentration of reactant:
  • A
    Is independent of time
  • B
    Varies linearly with time
  • ✓
    Varies exponentially with time
  • D
    None

Answer: C.

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Q 5M.C.Q (1 Marks)1 Mark
For a hypothetical reaction$:\ A + B \rightarrow $ Products, the rate law is $r = k[A][B]^0.$ The order of reaction is:
  • A
    $0$
  • ✓
    $1$
  • C
    $2$
  • D
    $3$

Answer: B.

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Q 61 Marks Question1 Mark
For the reaction R → P, the concentration of a reactant changes from 0.03M to 0.02M in 25 minutes. Calculate the average rate of reaction using units of time both in minutes and seconds.
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Q 71 Marks Question1 Mark
For a reaction, $\mathrm{A}+\mathrm{B} \rightarrow$ Product; the rate law is given by, $\mathrm{r}=\mathrm{k}[\mathrm{A}]^{1 / 2}[B]^2$. What is the order of the reaction?
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Q 81 Marks Question1 Mark
In a reaction, $2 \mathrm{~A} \rightarrow$ Products, the concentration of A decreases from $0.5 \mathrm{~mol} \mathrm{~L}^{-1}$ to $0.4 \mathrm{~mol} \mathrm{~L}^{-1}$ in 10 minutes. Calculate the rate during this interval?
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Q 112 Marks Questions2 Marks
A certain reaction is $50\%$ complete in $20$ minutes at $300\ K$ and the same reaction is again $50\%$ complete in $5$ minutes at $350\ K.$ Calculate the activation energy if it is a first order reaction. $[R = 8.314\ JK^{-1}\ mol^{-1},\ \log 4 = 0.602].$
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Q 122 Marks Questions2 Marks
How is the concept of coupling reactions useful in explaining the occurrence of non spontaneous thermochemical reactions? Explain giving an example.
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Q 132 Marks Questions2 Marks
For the first order thermal decomposition reaction, the following data were obtained:
$\text{C}_{2}\text{H}_{5}\text{Cl}\text{(g)}\rightarrow \text{C}_{2}\text{H}_{4}\text{(g)} + \text{HCl}\text{(g)} $
Time/sec Total pressure/atm
$0$ $0.30$
$300$ $0.50$
Calculate the rate constant
$($Given: $\log 2 = 0.301, \log 3=0.4771, \log 4 =0.6021)$
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Q 142 Marks Questions2 Marks
A first order reaction takes 20 minutes for 25% decomposition. Calculate the time when 75% of the reaction will be completed. (Given : log 2 = 0·3010, log 3 = 0·4771, log 4 = 0·6021)
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Q 152 Marks Questions2 Marks
The following data were obtained during the first order thermal decomposition of $SO_2Cl_2$ at a constant volume:
$SO_2Cl_2(g)$
$\rightarrow SO_2(g) + Cl_2(g)$
Experiment
Time/s$^{–1}$
Total pressure/atm
$1$
$0$
$0.4$
$2$
$100$
$0.7$
Calculate the rate constant.
$($Given: $\log 4 = 0.6021, \log 2 = 0.3010).$
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Q 163 Marks Question3 Marks
A certain reaction is $50 \%$ complete in 20 minutes at 300 K and the same reaction is again $50 \%$ complete in 5 minutes at 350 K . Calculate the activation energy if it is a first order reaction. $\left[R=8.314 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}\right.$, log $\left.4=0.602\right]$.
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Q 173 Marks Question3 Marks
How is the concept of coupling reactions useful in explaining the occurrence of non spontaneous thermochemical reactions? Explain giving an example.
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Q 183 Marks Question3 Marks
For the first order thermal decomposition reaction, the following data were obtained:
$\text{C}_{2}\text{H}_{5}\text{Cl}\text{(g)}\rightarrow \text{C}_{2}\text{H}_{4}\text{(g)} + \text{HCl}\text{(g)} $
Time/sec Total pressure/atm
0 0.30
300 0.50
Calculate the rate constant
(Given: log 2 = 0.301, log 3=0.4771, log 4 =0.6021)
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Q 193 Marks Question3 Marks
A first order reaction takes 20 minutes for 25% decomposition. Calculate the time when 75% of the reaction will be completed. (Given : log 2 = 0·3010, log 3 = 0·4771, log 4 = 0·6021)
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Q 203 Marks Question3 Marks
The following data were obtained during the first order thermal decomposition of $SO_2Cl_2$ at a constant volume:
$SO_2Cl_2(g) \rightarrow SO_2(g) + Cl_2(g)$
Experiment
Time/s$^{–1}$
Total pressure/atm
$1$
$0$
$0.4$
$2$
$100$
$0.7$
Calculate the rate constant.
$($Given: $\log 4 = 0.6021, \log 2 = 0.3010).$
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Q 22Case study (4 Marks)4 Marks
Decrease in concentration of reactant or increase in concentration of product per unit time is called rate of reaction. lt is of two types:
  1. Instantaneous rate of reaction: Rate of change of concentration of reactant or product at a particular time is called instantaneous rate of reaction.
$\text{r}_\text{inst.}=\frac{\text{dC}}{\text{dt}}$
where, dC = infinitely small change in concentration
dt = infinitely small change in time.
  1. Average rate of reaction: Ratio of change in concentration and time required for the change is average rate of reaction.
$\text{r}_\text{av}=\frac{\triangle\text{x}}{\triangle\text{t}}=\frac{\text{Change in concentration}}{\text{Time required for the change}}$
For a reaction of the type, $m_1A + m_2B → n_1C + n_2D$
Rate of reaction is given as
$\frac{1}{\text{m}_1}\frac{\text{d[A]}}{\text{dt}}=-\frac{1}{\text{m}_2}\frac{\text{d[B]}}{\text{dt}}=+\frac{1}{\text{n}_1}\frac{\text{d[C]}}{\text{dt}}=+\frac{1}{\text{n}_2}\frac{\text{d[D]}}{\text{dt}}$
In these questions (Q. No. i-iv), a statement of assertion followed by a statement ofreason is given. Choose the correct answer out of the following choices.
  1. Assertion and reason both are correct statements and reason is correct explanation for assertion.
  2. Assertion and reason both are correct statements but reason is not correct explanation for assertion.
  3. Assertion is correct statement but reason is wrong statement.
  4. Assertion is wrong statement but reason is correct statement.
  1. Assertion: The kinetics of the reaction, $\text{mA}+\text{nB}+\text{pC}\rightarrow\text{m}'\text{ X}+\text{n}'\text{ Y}+\text{p}'\text{ Z}$ obey the rate expression as $\frac{\text{dx}}{\text{dt}}=\text{k}[\text{A}]^\text{m}[\text{B}]^\text{n}.$
Reason: The rate of the reaction does not depend upon the concentration of C.
  1. Assertion: Instantaneous rate of reaction is equal to $\frac{\text{dx}}{\text{dt}}.$
Reason: lt is the rate of reaction at any particular instant of time.
  1. Assertion: For the reaction, $\text{RCl}+\text{NaOH}\rightarrow\text{ROH}+\text{NaCl},$ the rate of reaction is reduced to half on reducing the concentration of RCl to half.
Reason: The rate of reaction is represented by k[RCl].
  1. Assertion: ln rate law, unlike in the expression for equilibrium constants, the exponents for concentrations do not necessarily match the stoichiometric coefficients.
Reason: It is the mechanism and not the balanced chemical equation for the overall change that governs the reaction rate.
  1. Assertion: ln a reaction, $2A + B → A_2B$, the reactant B will disappear at twice the rate as A will decrease.
Reason: The rate of disappearance of reactant will be $-\frac{1}{2}\frac{\text{d[A]}}{\text{dt}}=-\frac{\text{d[B]}}{\text{dt}}$
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Q 23Case study (4 Marks)4 Marks
The following reaction, $\text{A}_{(\text{g})}\xrightarrow{\ \ \triangle\ \ \ }\text{P}_{(\text{g})}+\text{Q}_{(\text{g})}+\text{R}_{(\text{g})},$ follows first order kinetics. The half-life period of this reaction is $69.3s$ at $500^\circ C$. The gas A is enclosed in a container at $500^\circ C$ and at a pressure of $0.4$ atm.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. The rate constant for the reaction is:
  1. $0.4s^{-1}$
  2. $0.02s^{-1}$
  3. $0.01s^{-1}$
  4. $0.3s^{-1}$
  1. The pressure of the gas $A$ after $230$ s will be:
  1. $0.04$ atm
  2. $0.36$ atm
  3. $0.4$ atm
  4. $0.036$ atm
  1. The total pressure of the system after $230$ swill be:
  1. $2.15$ atm
  2. $1.12$ atm
  3. $0.4$ atm
  4. $3.08$ atm
  1. The plot ofln[A] vs twill be:
  1. Linear with slope $= k$
  2. Linear with intercept $= In[A]_0$
  3. Linear with slope $= In[A]_0$
  4. Linear with intercept $= [A]_0$
  1. Which of the following is not an example of first order reaction?
  1. $\text{C}_2\text{H}_{4(\text{g})}+\text{H}_{2(\text{g})}\rightarrow\text{C}_2\text{H}_{6(\text{g})}$
  2. $2\text{N}_2\text{O}_{5(\text{g})}\rightarrow4\text{NO}_{2(\text{g})}+\text{O}_{2(\text{g})}$
  3. $2\text{N}\text{H}_{3(\text{g})}\xrightarrow[\triangle]{\text{pt}}\text{N}_{2(\text{g})}+3\text{H}_{2(\text{g})}$
  4. $2\text{N}_2\text{O}_{(\text{g})}\xrightarrow{\ \ \triangle\ \ }2\text{N}_{2(\text{g})}+\text{O}_{2(\text{g})}$
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Q 24Case study (4 Marks)4 Marks
Number of molecules which must collide simultaneously to give product is called molecularity. It is equal to sum of coefficients of reactants present in stoichiometric chemical equation.
For reaction, $m_1A + m_2B \rightarrow$ Product
Molecularity $= [m_1 + m_2]$
ln complex reaction each step has its own molecularity which is equal to the sum of coefficients of reactants present in a particular step. Molecularity is a theoretical property. Its value is any whole number. Number of concentration terms on which rate of reaction depends is called order of reaction or sum of powers of concentration terms present in the rate equation is called order of reaction.
If rate equation ofreaction is: Rate $=\text{k}\cdot\text{C}^{\text{m}_1}_\text{A}\cdot\text{C}^{\text{m}_2}_\text{B}$
Then order of reaction $= m_1 + m_2.$
ln simple reaction, order and molecularity are same.
ln complex reaction, order of slowest step is the order ofover all reaction. This step is known as rate determining step. Order is an experimental property. Its value may be zero, fractional or negative.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. Higher order$(> 3)$ reactions are rare due to:
  1. Shifting of equilibrium towards reactants due to elastic collisions.
  2. Loss of active species on collision.
  3. Low probability of simultaneous collision of all the reacting species.
  4. Increase in entropy and activation energy as more molecules are involved.
  1. The molecularity of the reaction:
$6\text{FeSO}_4+3\text{H}_2\text{SO}_4+\text{KClO}_3\rightarrow\text{KCl}+3\text{Fe}_2(\text{SO}_4)_3+3\text{H}_2\text{O}$ is:
  1. $6$
  2. $10$
  3. $3$
  4. $7$
  1. Which of the following statements is false in the following?
  1. Order of a reaction may be even zero.
  2. Molecularity of a reaction is always a whole number.
  3. Molecularity and order always have same values for a reaction.
  4. Order of a reaction depends upon the mechanism of the reaction.
  1. The rate of reaction, $A + 2B →$ products, is given by the following equation:
$-\frac{\text{d}[\text{A}]}{\text{dt}}=\text{k}[\text{A}][\text{B}]^2$

If $B$ is present in large excess, the order of the reaction is:
  1. Zero
  2. First
  3. Second
  4. Third
  1. The rate of the reaction, $A + B + C →$ products, is given by $\text{r}=\frac{\text{d}[\text{A}]}{\text{dt}}=\text{k}[\text{A}]^\frac{1}{2}[\text{B}]^\frac{1}{3}[\text{C}]^\frac{1}{4}.$ The order of the reaction is:
  1. $\frac{1}{3}$
  2. $\frac{1}{4}$
  3. $\frac{1}{2}$
  4. $\frac{13}{12}$
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Q 25Case study (4 Marks)4 Marks
A reaction is said to be of the first order if the rate of the reaction depends upon one concentration term only. For a first order reaction of the type $A →$ Products, the rate of the reaction is given as: rate $= k[A]$. The differential rate law is given as: $\frac{\text{dA}}{\text{dt}}=-\text{k}[\text{A}].$ The integrated rate law is: In $\frac{[\text{A}]}{[\text{A}]_0}=-\text{kt},$ [A] is the concentration of reactant left at time t and $[A]_0$ is the initial concentration of the reactant, k is the rate constant.
The following questions are multiple choice questions. Choose the most appropriate answer:
  1. The unit of rate constant for a first order reaction is:
  1. $S^{-1}$
  2. $mol L^{-1} s^{-1}$
  3. $L mol^{-1} s^{-1}$
  4. $L^2 mol^{-2} s^{-1}$
  1. Half-life period of a first order reaction is $10min$. Starting with initial concentration $12M$, the rate after 20min is:
  1. $0.693 \times 3M min^{-1}$
  2. $0.0693 \times 4M min^{-1}$
  3. $0.0693 \times M min^{-1}$
  4. $0.0693 \times 3M min^{-1}$
  1. $50\%$ of a first order reaction is complete in $23$ minutes. Calculate the ti me required to complete $90\%$ of the reaction.
  1. $70.4$ minutes.
  2. $76.4$ minutes.
  3. $38.7$ minutes.
  4. $35.2$ minutes.
  1. For a first order reaction, $(A) → $ products, the concentration of A changes from $0.1M$ to $0.025M$ in $40$ minutes. The rate of reaction when the concentration of A is $0.01M$, is:
  1. $3.47 \times 10^{-4} M/ min$
  2. $3.47 \times 10^{-5} M/ min$
  3. $1.73 \times 10^{-4} M/ min$
  4. $1.73 \times 10^{-5} M/ min$
  1. The half-life period ofa 1st order reaction is $60$ minutes. What percentage will be left over after $240$ minutes?
  1. $6.25\%$
  2. $4.25\%$
  3. $5\%$
  4. $6\%$
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Q 265 Marks Questions5 Marks
The rate constant for the first order decomposition of $H_2O_2$​​​​​​​ is given by the following equation:
log $k = 14.34 – 1.25 \times 10^4K/T$
Calculate $E_a​​​​​​​$​​​​​​​ for this reaction and at what temperature will its half-period be $256$ minutes?
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Q 275 Marks Questions5 Marks
The experimental data for decomposition of $N_2O_5 [2N_2O_5 \rightarrow 4NO_2 + O_2]$ in gas phase at $318K$ are given below:
$t/s$ $0$ $400$ $800$ $1200$ $1600$ $2000$ $2400$ $2800$ $3200$
$10^2 \times [N_2O_5]/mol L^{-1}$ $1.63$ $1.36$ $1.14$ $0.93$ $0.78$ $0.64$ $0.53$ $0.43$ $0.35$
  1. Plot $[N_2O_5]$ against t.
  2. Find the half-life period for the reaction.
  3. Draw a graph between $\log[N_2O_5]$ and $t.$
  4. What is the rate law?
  5. Calculate the rate constant.
  6. Calculate the half-life period from k and compare it with $(ii).$
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Q 285 Marks Questions5 Marks
The rate constant for the decomposition of $N_2O_5$ at various temperatures is given below:
$T/^\circ C$ $0$ $20$ $40$ $60$ $80$
$105 \times k/s-1$ $0.0787$ $1.70$ $25.7$ $178$ $2140$
Draw a graph between ln $k$ and $1/T$ and calculate the values of $A$ and $E_a$. Predict the rate constant at $30^\circ$ and $50^\circ C.$
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Q 295 Marks Questions5 Marks
The time required for $10 \%$ completion of a first order reaction at $298 K$ is equal to that required for its $25 \%$ completion at $308 K $. If the value of A is $4 \times 10^{10} S^{-1}$. Calculate k at $318 K $ and $E _{ a }$.
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Q 305 Marks Questions5 Marks
Match the graph given in Column I with the order of reaction given in Column II. More than one item in Column I may link to the same item of Column II.
 
Column I
 
Column II
(i)
 
 
(ii)
(a)
$I^{st}$ order
(iii)
(b)
Zero order
(iv)
   
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