Tag: rates of reaction

Questions Related to rates of reaction

$C _{4}H _{8}\rightarrow 2C _{2}H _{4}$; rate constant $=2.303\times 10^{4}\sec^{-1}$, After what time the molar ratio of $\dfrac{C _{2}H _{4}}{C _{4}H _{8}}$ attain the value $1$

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

  1. $176\ sec$

  2. $3522\ sec$

  3. $1661\ sec$

  4. $1761\ sec$

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Correct Option: A

In which of the following cases, the reaction goes farthest to completion?

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

  1. $A \rightleftharpoons B (K = 10^3)$

  2. $P \rightleftharpoons Q (K = 10^{-2})$

  3. $A + B \rightleftharpoons C + D (K = 10)$

  4. $X + Y \rightleftharpoons XY _2 (K = 10^{-1})$

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Correct Option: A
Explanation:

Higher the equilibrium constant, faster the rate of reaction

$A+B \rightleftharpoons C+D$
$\Rightarrow K=\cfrac {[C][D]}{[A][B]}$
To complete the reaction fastest the numerator of $RHS$ will be higher.
$\therefore$ Option A 
$A\rightleftharpoons B(K=10^3)$ is correct, because equilibrium constant in option A is higher than remaining options.

On increasing the pressure three fold, the rate of reaction of ${ 2H } _{ 2 }{ S }$ + ${ O } _{ 2 }$ $\rightarrow $ products would increase

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

  1. 3 times

  2. 9 times

  3. 12 times

  4. 27 times

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Correct Option: D
Explanation:

Rate$=$ ${K _{{p^2}}}{H _2}S \times P{O _2} = x$ $($rate$)$


On increasing the pressure three fold :


Rate$=$ $K{\left( {3{P _{{H _2}S}}} \right)^2}\left( {3P{O _2}} \right)$

$=$ $K \times 9{P^2} _{{H _2}S} \times 3P{O _2}$

$=$ $K \times 27 \times {P _{{H _2}S}} \times P{O _2} = 27$

the rate will increases $27$ times 

Hence, option $(D)$ is correct answer.

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

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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 $III$

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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.

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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

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Correct Option: B
Explanation:

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

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