Tag: rate of reaction

Questions Related to rate of reaction

Negative sign denotes that the concentration of reactant is                     with time.

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

  1. decreasing

  2. increasing

  3. heating up

  4. cooling up

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Correct Option: A
Explanation:

The speed of a chemical reaction may be defined as the change in concentration of a substance divided by the time interval during which this change is observed. Definition of a rate of reaction. We, in general, use a negative sign for reactants because its concentration is decreasing as the chemical reaction is taking place.

In a reaction $2X \rightarrow Y$, the concentration of $X$ decreases from $3.0$ moles/ litre to $2.0\ moles/ litre$ in $5$ minutes. The rate of reaction is :

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

  1. $0.1\ mol\ L^{-1} min^{-1}$

  2. $5\ mol\ L^{-1} min^{-1}$

  3. $1\ mol\ L^{-1} min^{-1}$

  4. $0.5\ mol\ L^{-1} min^{-1}$

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Correct Option: A
Explanation:

$Rate = -\dfrac {1}{2} \dfrac {\triangle [X]}{\triangle t}$
$= -\dfrac {1}{2} \dfrac {(3 - 2)}{5} = -0.1\ mol\ L^{-1} min^{-1}$
Negative sign signifies the decrease in concentration.

The rate law for a reaction, $A + B \rightarrow C + D$ is given by the expression $k[A]$. The rate of reaction will be:

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

  1. doubled on doubling the concentration of $B$

  2. halved on reducing the concentration of $A$ to half

  3. decreased on increasing the temperature of the reaction

  4. unaffected by any change in concentration of temperature

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Correct Option: B
Explanation:

Rate of reaction- The speed at which a chemical reaction proceeds, It is often expressed in terms of either the concentration (amount per unit volume) of a product that is formed in a unit of time or the concentration of a reactant that is consumed in a unit of time.

other terms of expression are produced or consumed $\dfrac{mol}{time}$ and in case of gas we can use pressure term also.
So the correct option is $[B]$

Which of the following expressions is correct for the rate of reaction given below?


$5Br^{-} _{(aq)} + BrO _{3(aq)}^{-} + 6H^{+} _{(aq)} \rightarrow 3Br _{2(aq)} + 3H _{2}O _{(l)}$

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

  1. $\dfrac {\triangle [Br^{-}]}{\triangle t} = 5\dfrac {\triangle [H^{+}]}{\triangle t}$

  2. $\dfrac {\triangle [Br^{-}]}{\triangle t} = \dfrac {6}{5}\dfrac {\triangle [H^{+}]}{\triangle t}$

  3. $\dfrac {\triangle [Br^{-}]}{\triangle t} = \dfrac {5}{6}\dfrac {\triangle [H^{+}]}{\triangle t}$

  4. $\dfrac {\triangle [Br^{-}]}{\triangle t} = 6\dfrac {\triangle [H^{+}]}{\triangle t}$

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Correct Option: C
Explanation:

For the reaction,


$5Br^{-} _{(aq)} + BrO _{3(aq)}^{-} + 6 _{(aq)}^{+} \rightarrow 3Br _{2(aq)} + 3H _{2}O _{(l)}$


Rate of disappearance $= \dfrac {-1}{5}\dfrac {\triangle [Br^{-}]}{\triangle t} = -\dfrac {\triangle [BrO _{3}^{-}]}{\triangle t} = \dfrac {-1}{6} \dfrac {\triangle [H^{+}]}{\triangle t}$

$ \dfrac {\triangle [Br^{-}]}{\triangle t} = \dfrac {5}{6} \dfrac {\triangle [H^{+}]}{\triangle t}$.

Hence, the correct answer is option $\text{C}$.

The rate of reaction usually decreases with time.

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

  1. True

  2. False

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Correct Option: A
Explanation:

The speed of a chemical reaction may be defined as the change in concentration of a substance divided by the time interval during which this change is observed. Hence rate of reaction is inversely related as the time increases rate of reaction decreases. Hence given statement is true.

The rate of a gaseous reaction is given by the expression $k[A]^{2}[B]^{3}$. The volume of the reaction vessel is reduced to one half of the initial volume. What will be the reaction rate as compared to the original rate $a$?

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

  1. $\dfrac {1}{8}a$

  2. $\dfrac {1}{2}a$

  3. $2a$

  4. $32a$

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Correct Option: D
Explanation:

$Rate = k[A]^{2} [B]^{3} = a$


When volume is reduced to one half then conc. of reactants will be doubled.

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

         $=32 k[A]^{2} [B]^{3} = 32a$.

So, the correct option is $D$

In a reaction, $2X \rightarrow Y$, the concentration of $X$ decreases from $0.50\ M$ to $0.38\ M$ in $10\ min$. What is the rate of reaction in $M\ s^{-1}$ during this interval?

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

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

  2. $4\times 10^{-2}$

  3. $2\times 10^{-2}$

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

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Correct Option: A
Explanation:

Rate of reaction $= \dfrac {\triangle [X]}{\triangle t}$


$\triangle [X] = X _{i} - X _{f} = 0.50 - 0.38 = 0.12\ M$

$Rate = \dfrac {0.12}{10\times 60} = 2\times 10^{-4} M\ s^{-1}$.

The rate equation for a reaction is r =  $K[A]^{\circ}[B]^3$. Which of the following statements are true?

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

  1. Doubling the concentration of B quadruples the rate of reaction

  2. The units of rate constant are mole$^{-2} L^2 S^{-1}$

  3. The plot of concentration of A Vs time is parallel to the time axis

  4. If the volume of the reaction vessel is decreased to $\frac{1}{3}$, the rate of reaction is $ \frac{1^th}{27}$ of the original rate

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Correct Option: B,C
Explanation:

$r= K[A]^{o} $ $[B]^3$

The reaction is zero order with respect $A$  and order with respect to $B$ is 3. The overall order being 3, the units of the rate constant are mole $^{-2}$l$^2$ s$^{-1}$. The rate of reaction does not change with a change in concentration of $A$. Therefore, the plot of concentration of $A$ vs time is parallel to a time axis. If the volume of the reaction vessel is decreased to $\frac{1}{3}$, the rate of reaction is 27 times of the original rate.

The reaction $A(g)+2B(g)\rightarrow C(g)+D(g)$ is an elementary process. In an experiment, the initial partial pressure of $A$ and $B$ are $P _A=0.6$ and $P _B=0.8$ atm 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. $\dfrac{1}{48}$

  2. $\dfrac{1}{24}$

  3. $\dfrac{9}{16}$

  4. $\dfrac{1}{16}$

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Correct Option: D
Explanation:

$ \implies \space \space \space A(g) \space \space \space \space \space \space+ \space \space \space \space \space \space 2B(g) \rightarrow \space \space \space \space \space \space \space \space C(g) + D(g) $
$ At \space t=0 \space0.6 \space \space \space \space \space \space \space \space \space \space \space \space \space \space \space \space \space 0.8 \space \space \space \space \space \space \space \space \space \space \space \space \space \space \space \space \space \space \space \space 0 \space \space \space \space \space \space \space \space \space \space \space \space \space 0 $
$ At \space t=t \space (0.6-0.2) \space \space \space \space (0.8 - 2 \times 0.2) \space \space 0.2 \space \space \space \space \space \space \space \space \space \space0.2$

$ Rate _i = [0.6][0.8]^2$
$ Rate _t = [0.4][0.4]^2$
$ \dfrac{Rate _t}{Rate _i} = \dfrac{1}{6}$

Which does not affect the rate of a reaction?

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

  1. Nature of the reactants

  2. Time

  3. Concentrations

  4. Surface area exposed

  5. Temperature

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Correct Option: B
Explanation:

Time does not affect the rate of a reaction. Hence, in the rate law expression $ \displaystyle rate = k[A]^n$, there is no term for time.
Nature of the reactants, Concentrations, surface area exposed and temperature affects  the rate of a reaction.