Tag: reaction kinetics

Quizzes (1) Questions (19)

Questions Related to reaction kinetics

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

When a chemical reaction takes place, during the course of the reaction the rate of reaction?

  1. Keeps on increasing with time

  2. Remains constant with time

  3. Keeps on decreasing with time

  4. Shows irregular trend with time
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Rate of reaction $\propto$ conc. of reactants
As the reaction proceeds, concentration of the reactants decreases hence the rate also keeps on decreasing with time.

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

In a reaction $2HI \rightarrow H _{2} + I _{2}$, the concentration of $HI$ decreases from $0.5\ mol\ L^{-1}$ to $0.4\ mol\ L^{-1}$ in $10$ minutes. What is the rate of reaction during this interval?

  1. $5\times 10^{-3} M\ min^{-1}$
  2. $2.5\times 10^{-3} M\ min^{-1}$
  3. $5\times 10^{-2} M\ min^{-1}$
  4. $2.5\times 10^{-2} M\ min^{-1}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Average rate $= -\dfrac {1}{2} \dfrac {\triangle [R]}{\triangle t} = -\dfrac {1}{2}\times \dfrac {0.4 - 0.5}{10}$


$= \dfrac {1}{2}\times \dfrac {0.1}{10} = 5\times 10^{-3}M\ min^{-1}$.

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

Which of the following statements is correct?

  1. The rate of a reaction decreases with passage of time as the concentration of reactants decreases.

  2. The rate of a reaction is same at any time during the reaction.

  3. The rate of a reaction is independent of temperature change.

  4. The rate of a reaction decreases with increase in concentration of reaction(s).
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

According to rate law expression,
$Rate \propto [R]$
Thus, rate of a reaction decreases with passage of time as the concentration of reactants decreases.

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

Consider the chemical reaction:
$N _2(g)+3H _2(g)\rightarrow 2NH _3(g)$


The rate of this reaction can be expressed; in terms of time and of concentration of $N _2(g), H _2(g)$ $NH _3(g)$. Identify the correct relationship amongst the rate expressions.

  1. Rate $=-\dfrac{d[N _2]}{dt}=-\dfrac{1}{3}\dfrac{d[H _2]}{dt}=+\dfrac{1}{2}\dfrac{d[NH _3]}{dt}$
  2. Rate $=-\dfrac{d[N _2]}{dt}=-\dfrac{3d[H _2]}{dt}=\dfrac{2d[NH _3]}{dt}$
  3. Rate $=-\dfrac{d[N _2]}{dt}=-\dfrac{1}{3}\dfrac{d[H _2]}{dt}=\dfrac{d[NH _3]}{dt}$
  4. Rate $=-\dfrac{d[N _2]}{dt}=\dfrac{d[H _2]}{dt}=\dfrac{d[NH _3]}{dt}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

As the reaction proceed, the concentration of the reactant decrease and that of the product increases.
Thus, the rate of the reaction of the reactant and product can be given as follow:
$Rate =-\cfrac{d}{dt}[N _2]=-\cfrac{1}{3}\cfrac{d}{dt}[H _2]=+\cfrac{1}{2}\cfrac{d}{dt}[NH _3]$

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

Rate of formation of $SO _3$ in the following reaction $2SO _2+O _2\rightarrow 2SO _3$ is $100g$ $min^{-1}$. 


Then the rate of disappearance of $O _2$ is:

  1. $50g$ $min^{-1}$
  2. $40g$ $min^{-1}$
  3. $200g$ $min^{-1}$
  4. $20g$ $min^{-1}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$2{ SO } _{ 2 }+{ O } _{ 2 }\rightarrow 2{ SO } _{ 3 }$


rate $=\dfrac { 1 }{ 2 } \dfrac { \left[ { \triangle SO } _{ 2 } \right]  }{ \triangle t } =\dfrac { \triangle \left[ { O } _{ 2 } \right]  }{ \triangle t } =\dfrac { 1 }{ 2 } \dfrac { \triangle \left[ { SO } _{ 3 } \right]  }{ \triangle t } $

rate of formation of ${ SO } _{ 3 }=$ rate of disappearance of ${ O } _{ 2 }$

$\dfrac { 1 }{ 2 } \dfrac { \triangle \left[ { SO } _{ 3 } \right]  }{ \triangle t } =-\dfrac { \triangle \left[ { O } _{ 2 } \right]  }{ \triangle t } $

$-\dfrac { \triangle w _{{ O } _{ 2 }}   }{ \triangle t }=\dfrac { 1 }{ 2 } \times \dfrac{100}{80}\times 32g{ min }^{ -1 }=20g{ min }^{ -1 }$

So, the correct option is $D$

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

If concentration of reactants is increased by a factor x then the rate constant k becomes:

  1. $\ln{\frac{k}{x}}$
  2. $\frac{k}{x}$
  3. $k+x$
  4. $k$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Rate Constant doesn't depend on the concentration of the reactants.

So, If the conc of reactants is increased by a factor x, then the rate constant k becomes k.

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

An aqueous solution of $CH _3COOH$ has a pH = $3$ and acid dissociation constant of $CH _3COOH$ is $10^{-5}$. What will be the concentration of acid taken initially?

  1. $0.1$M
  2. $0.11$M
  3. $0.09$M
  4. $0.101$M
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

${H}^{+} = \sqrt{{K} _{a} \times {C}}$


${10}^{-6} = {10}^{-5} \times {C}$

${C} = 0.1\space M$

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction

For the non-equilibrium process, $A + B \rightarrow Products$, the rate is first order with respect to $A$ and second-order with respect to $B$. If $1.0$ mole each of $A$ and $B$ are introduced into a 1-litre vessel and the initial rate was $1.0 \times 10^{-2}$ mol/litre-sec. The rate (in mol $litre^{-1} sec^{-1}$) when half of the reactants have been used:

  1. $1.2 \times 10^{-3}$
  2. $1.2 \times 10^{-2}$
  3. $2.5 \times 10^{-4}$

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

$rate = k[A]{[B]}^{2}$


Initially 1 mol each of A and B are present and the rate was $1 \times {10}^{-2}\space mol/lit-sec$

When Half of the Reactants are used, the rate becomes $\dfrac{1}{2} \times {[\dfrac{1}{2}]}^{2} \times {10}^{-2}$ = $1.2 \times {10}^{-3}$

Multiple choice chemistry reaction kinetics determining rates graphically calculating rate of reaction graphically rate of a chemical reaction
 Time  0  5min  10min  15min
 [A]  20mol  18mol  16mol  16 mol

For the reaction $A\longrightarrow Products$; $\frac { -d[A] }{ dt } =k$ and at different time interval, IAI values are given. At $20$ minute, rate will be :

  1. $12 mol /min$
  2. $10 mol/min$
  3. $8 mol/min$
  4. $0.4 mol/min$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The concentration decreases linearly with time

Hence moles of A at $20 min$
$=12$
Therefore, $k=\dfrac{-d[A]}{dt}$
$=-\dfrac{12-14}{20-15}$
$=0.4\ mol/min$