Tag: rates of reaction

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Questions Related to rates of reaction

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

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

  1. decreasing

  2. increasing

  3. heating up

  4. cooling up
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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 :

  1. $0.1\ mol\ L^{-1} min^{-1}$
  2. $5\ mol\ L^{-1} min^{-1}$
  3. $1\ mol\ L^{-1} min^{-1}$
  4. $0.5\ mol\ L^{-1} min^{-1}$
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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 $[B]$

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

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


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

  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. $\dfrac {\triangle [Br^{-}]}{\triangle t} = 6\dfrac {\triangle [H^{+}]}{\triangle t}$
Reveal answer Fill a bubble to check yourself
C Correct answer
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 $\text{C}$.

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

The rate of reaction usually decreases with time.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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 $a$?

  1. $\dfrac {1}{8}a$
  2. $\dfrac {1}{2}a$
  3. $2a$
  4. $32a$
Reveal answer Fill a bubble to check yourself
D Correct answer
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 $D$

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

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?

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

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


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

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

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

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

  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
Reveal answer Fill a bubble to check yourself
B,C Correct answer
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.

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

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:

  1. $\dfrac{1}{48}$
  2. $\dfrac{1}{24}$
  3. $\dfrac{9}{16}$
  4. $\dfrac{1}{16}$
Reveal answer Fill a bubble to check yourself
D Correct answer
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}$

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

Which does not affect the rate of a reaction?

  1. Nature of the reactants

  2. Time

  3. Concentrations

  4. Surface area exposed

  5. Temperature
Reveal answer Fill a bubble to check yourself
B Correct answer
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.