Tag: rates of reaction

Questions Related to rates of reaction

For a chemical reaction, $A \rightarrow products$, the rate of reaction doubles when the concentration of A is increased by a factor of 4, the order of reaction is :

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

  1. 2

  2. 0.5

  3. 4

  4. 1

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Correct Option: B
Explanation:
let x be order of reaction and K be rate of constant.
* A$\rightarrow $ products.
$ \cfrac { K\cfrac { { \left( A \right)  }^{ x } }{ time }  }{ K\cfrac { { \left( 4A \right)  }^{ x } }{ time }  } or,\quad \cfrac { 1 }{ 2 } = { \left( \cfrac { A }{ 4A }  \right)  }^{ x }\\ or,\quad \cfrac { 1 }{ 2 } ={ \left( \cfrac { 1 }{ 4 }  \right)  }^{ x }$      (reciprocating)
$\\ or,\quad 2={ \left( 4 \right)  }^{ x }\\ or,\quad 2={ { 2 }^{ 2 } }^{ x }\\ or,\quad 2x=1\\ or,\quad x=\cfrac { 1 }{ 2 } \\ x=0.5$

The term $-\dfrac{dc}{dt}$ in a rate equation refers to:

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

  1. the concentration of a reactant

  2. the decrease in concentration of the reactant with time

  3. the velocity constant of reaction

  4. none of the above

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Correct Option: B
Explanation:

The term $-\dfrac{dc}{dt}$ in a rate expression indicates the decrease in concentration of the reactant with time. It is the minus sign which is used to show the decrease in concentration of the reactant.

For a first order reaction, A$\rightarrow$ products, the concentration of A changes from $0.1$M to $0.025$ M $80$ minutes. The rate of reaction when the concentration of A is $0.01$M, is:

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

  1. $1.73\times 10^{-5}$M/min

  2. $3.47\times 10^{-4}$M/min

  3. $3.47\times 10^{-5}$M/min

  4. $1.73\times 10^{-4}$M/min

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Correct Option: D
Explanation:

K$= \frac { 2.303 }{ t } \log { \left[ \dfrac { { A } _{ 0 } }{ A }  \right]  } $


$\quad =\dfrac { 2.303 }{ 80 } \log [{ \dfrac { 0.1 }{ 0.025 }  }]$

$k= 0.0173\quad { min }^{ -1 }$

$\therefore $ Rate$= K\left[ A \right]$

$\quad \quad \quad =0.0173\left[ 0.01 \right]$

$\quad \quad \quad = 1 .73 \times { 10 }^{ -4 } $

$\quad \quad \quad =1.73\times{ 10 }^{ -4 }M/min$

Hence, the correct option is $(D)$

Which of the following is (are) true for first order reaction?

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

  1. Rate of reaction is fastest at the beginning of reaction.

  2. Rate of reaction is fastest when (reactants)=(products)

  3. Rate of reaction increases with temperature

  4. Ea decreases considerably as temperature as temperature increases, hence the reaction becomes faster

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Correct Option: A,C
Explanation:

A] True. for first order reactions, products are formed at the fastest rate during the  beginning of the reaction.

B] False. When reactants>Products, the rate of reaction is fast.
C] True. Increasing the temperature increases the rate of reaction.
D] False. Activating energy does not decrease, but increasing the temperature allows crossing of energy barrier.

If enthalpy of $B$ is greater than that of $A$, the reaction $A\rightarrow B$ will be:

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

  1. instantaneous

  2. exothermic

  3. endothermic

  4. spontaneous

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Correct Option: C
Explanation:

In an endothermic reaction, the enthalpy of the product is greater than the enthalpy of the reactant. 

Thus, the given reaction is an endothermic reaction.

For the reaction $2A + B + C \rightarrow 2D$. The observed rate law is Rate=$K[A]{ [B] }^{ 2 }$. Correct statements are
a) An increase of cone .of C does not affect the rate
b)Doubling the conc of A doubles the rate
c)Tripling the conc of B increases the rate by 9 times
d)Doubling the conc of C, doubling the rate

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

  1. a,b,c

  2. b,c,d

  3. d

  4. c,d

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Correct Option: A
Explanation:

Given  rate is $k[A]{ [B] }^{ 2 }$

 It is overall ${ 3 }^{ rd }$ order  reaction with a following  first order  and B following second order.
 (a) True  C is not affecting the rate of reaction.
 (b) True $rate _{ 1 }\quad =k[A]{ [B] }^{ 2 }\ rate _{ 2 }\quad =k[2A]{ [B] }^{ 2 }=2k[A]{ [B] }^{ 2 }\ =2\times rate _{ 1 }$
 (c) True $rate _{ 1 }\quad =k[A]{ [B] }^{ 2 }\ rate _{ 3 }=k[A]{ [3B] }^{ 2 }=9Kk[A]{ [B] }^{ 2 }\ =9\times rate _{ 1 }$
(d)False C does not affected  the rate in any manner.

${ SO } _{ 2 }$ react with ${ O } _{ 2 }$ as follows :


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


The rate of disappearance of ${ SO } _{ 2 }$ is $2.4\times { 10 }^{ -4 }$ mol ${ lit }^{ -1 }{ min}^{ -1 }$, then :

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

  1. Rate of reaction is $1.2\times { 10 }^{ -4 }\quad mole{ lit }^{ -1\quad }{ min }^{ -1 }$

  2. Rate of appearance of ${ SO } _{ 3 }$ is $2.4\times { 10 }^{ -4 } { mole\quad lit }^{ -1 }min^{ -1 }$

  3. Rate of disappearance of ${ O } _{ 2 }$ is $1.2\times { 10 }^{ -4 } { mole\quad lit }^{ -1 }min^{ -1 }$

  4. Rate of reaction is twice the rate of disappearance of ${ SO } _{ 2 }$

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Correct Option: B,C,D

Which of the fallowing can enhance the rate of the reaction ?

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

  1. increasing the temperature

  2. increasing the concentration of products

  3. increasing the activation energy

  4. using a +Ve catalyst

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Correct Option: A,D
Explanation:

Solution:- (A) increasing the temperature and (D) using a +ve catalyst
  • Temperature is a measure of the kinetic energy of a system, so higher temperature implies higher average kinetic energy of molecules and more collisions per unit time. Hence an increase in temperature is accompanied by an increase in the reaction rate. 
  • A higher concentration of reactants leads to more effective collisions per unit time, which leads to an increased reaction rate (except for zero order reactions). Similarly, a higher concentration of products tends to be associated with a lower reaction rate.
  • Catalysts (e.g., enzymes) lower the activation energy of a chemical reaction and increase the rate of a chemical reaction without being consumed in the process. 
  • Hence, using a positive catalyst and increasing the temperature, both can enhance the rate of reaction.

By the action of enzymes, the rate of biochemical reaction:

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

  1. does not change

  2. increases

  3. decreases

  4. Either $a$ or $c$

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Correct Option: B
Explanation:

Enzymes are the very efficient catalyst for the enzymatic biochemical reaction and Enzymes speed up the reaction by providing lower activation energy.

Rate of formation of $SO _{3}$ according to the reaction $2SO _{2}+O _{2} \rightarrow 2SO _{3}$ is $1.6 \times 10^{-3}\ kg\ min^{-1}$ Hence rate at which $SO _{2}$ reacts is :-

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

  1. $1.6 \times 10^{-3}\ kg\ min^{-1}$

  2. $8.0 \times 10^{-4}\ kg\ min^{-1}$

  3. $3.2 \times 10^{-3}\ kg\ min^{-1}$

  4. $1.28\times 10^{-3}\ kg\ min^{-1}$

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Correct Option: B