Tag: rate of chemical reaction

Questions Related to rate of chemical reaction

Which of the following is not a valid way to describe the rate of the following reaction?
$A + B + C \rightarrow D + E$

chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

  1. $\dfrac {-\triangle [A]}{\triangle t}$

  2. $\dfrac {-\triangle [B]}{\triangle t}$

  3. $\dfrac {-\triangle [C]}{\triangle t}$

  4. $\dfrac {-\triangle [D]}{\triangle t}$

  5. $\dfrac {-\triangle [E]}{\triangle t}$

Show answer
Correct Option: D,E
Explanation:

$A+B+C\longrightarrow D+E$

 Rate of reaction is defined as the change in concentration of reactant or product to time.
 Rate $ (R)=\cfrac { -d[A] }{ dt } =\cfrac { -d[B] }{ dt } =\cfrac { -d[C] }{ dt } =\cfrac { d[D] }{ dt } =\cfrac { d[E] }{ dt } $
Therefore, (D)  &  (E) i.e. $ \cfrac { -d[D] }{ dt } & \quad \cfrac { -d[E] }{ dt } $ respectively are not valid ways of describing the rate of the following reaction.

What is the rate-determining step?

chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

  1. The slowest step in the reaction.

  2. The fastest step in the reaction.

  3. The overall rate of the reaction.

  4. A law relating the steps of a reaction.

  5. The step which keeps on changing

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Correct Option: A
Explanation:

The slowest step in the mechanism of any reaction is the rate-determining step of the reaction.


Hence, the correct option is A.

Rate of reaction depends upon:

chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

  1. Temperature

  2. Concentration

  3. Catalyst

  4. All of these

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Correct Option: D
Explanation:

The rate of reaction depends upon the nature of reactants, the concentration of the reactants, temperature, and catalyst.

So, the correct option is $D$

${H} _{2}(g)+{I} _{2}(g)+51.9\ kilojoules\rightarrow 2HI(g)$
Which of the following can be expected to increase the rate of the reaction given by the equation above?
$I$. Adding some helium gas
$II$. Adding a catalyst
$III$. Increasing the temperature

chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

  1. $I$ only

  2. $III$ only

  3. $II$ only

  4. $II$ and $III$ only

  5. $I,II$ and $III$

Show answer
Correct Option: D
Explanation:

(i)   Addition of Helium gas will not increase the rate of reaction. It will either remain same or decrease depending upon 

      whether addition is done in constant volume or constant pressure conditions.
(ii)  Adding a catalyst will lower the activation energy and thus increase the value of the rate constant which will increase the rate.
(iii)  Increasing the temperature will also increase the value of rate constant and thus the rate of the reaction will increase.
                       $K=A{ e }^{ -Ea/RT }$
$\therefore $ only (ii) & (iii).

The rate of reaction for a concentrated strong acid with a concentrated strong base is least affected by which of the following?

chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

  1. The use of a catalyst.

  2. A change in temperature.

  3. A change in reactant concentration.

  4. A change in pressure.

Show answer
Correct Option: A
Explanation:

A change in pressure effects only if there is a difference between the number of moles of gaseous products & the number of moles of gaseous reactant. In short, a change in pressure affects only if there is at least one gas either in products or reactants. 

Reaction could be such as:


$ HCl(aq) + NaOH (aq) \rightarrow  NaCl(aq) + H _2O (l)$

As the reaction between concentrated acid and a base reactant or product takes place, there is least effect of change in pressure on the rate of reaction.

Hence, the correct option is D.


Which factor has no influence on the rate of reaction?

chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

  1. Molecularity

  2. Temperature

  3. Concentration of reactant

  4. Nature of reactant

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Correct Option: A

The rate constant of the relation $ A \rightarrow B $ is $ 0.6 \times 10^{-3} $ mole per second. If the concentration of $B$ after $20$ minutes is :

chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

  1. $0.36$ M

  2. $0.72$ M

  3. $1.08$ M

  4. $3.60$ M

Show answer
Correct Option: B
Explanation:

By unit of rate constant it is clear,that the $reaction$ is zero order. 

$\therefore \left [ B \right ]=k\times t$
         $=0.72M$

The rate law for a reaction between the substances $A$ and $B$ is given by rate$=k{ \left[ A \right]  }^{ n }{ \left[ B \right]  }^{ m }$. On doubling the concentration of $A$ and having the concentration of $B$ halved, the ratio of the new rate to the earlier rate of the reaction will be as:

chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

  1. $\cfrac { 1 }{ { 2 }^{ m+n } } $

  2. $(m+n)$

  3. $(n-m)$

  4. ${2}^{(n-m)}$

Show answer
Correct Option: D
Explanation:

Given that

                    $R=K[A]^n[B]^m$
after doubling the concentration of $A$ and concentration of $B$ is halfed 
$R^1=K[2A]^n[\dfrac{B}{2}]^m$
$R^1 =(2)^{n-m} R$
$ \dfrac{R^1}{R}= \dfrac{2^{n-m}}{1}$

The rate equation for the reaction $2A+B \rightarrow C$ is found to be rate = $k[A] [B]$. The correct statement in relation to this reaction is that the :

chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

  1. units of $k$ must be$\ mol^{-1} L$ $s^{-1}$.

  2. $t _{1/2}$ is constant

  3. rate of formation of C is twice the rate of disappearance of A

  4. value of $k$ is independent of the initial concentration of A and B

Show answer
Correct Option: A
Explanation:

The given reaction is $2A+B\longrightarrow C$

The given rate equation is:-
$rate=K[A] [B]$

The unit of rate is $mol L^{-1} s^{-1}$
Unit of $[A]= mol L^{-1}$
Unit of $[B]= mol L^{-1}$

Unit of $K$=$\cfrac {mol L^{-1} s^{-1}}{mol L^{-1} mol L^{-1}}$
$=mol^{-1} L$ $s^{-1}$.

The reaction $A(g)+2B(g)\rightarrow C(g)+D(g)$ is an elementary process. In an experiment in volving this reaction. The initial pressure of A and B are $P _A=0.6$ atm $P _B=0.8$atm respectively when $P _C=0.2$ atm, the rate of reaction relative to the initial rate is:

chemistry rates of reaction introduction to rate of reaction rate of chemical reaction rate of reaction

  1. $\displaystyle\frac{1}{6}$

  2. $\displaystyle\frac{1}{12}$

  3. $\displaystyle\frac{1}{36}$

  4. $\displaystyle\frac{1}{18}$

Show answer
Correct Option: A
Explanation:
        $A(g) + 2(B) \rightarrow C(g) + D(g)$
 t = 0  0.6         0.8              0     0
 at t     0.6-x      0.8-x          x       x
since this the elementary reaction
rate,r = $K[B]^2 [A]$
now $r _i = k (0.6)(0.8)^2 = 0.38K$
when $P _i = x - 0.2$ atm
when $P _A= 0.6-x =0.4$ atm
when $P _B= 0.8 - 2x =0.4$ atm
$r _f = K(0.4) (0.4)^2 = 0.064K$
$r _1/r _2 = 0.064/0.384 = 1/6$