Tag: dependence of reaction rate on concentration of reactants

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Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

The rate of the reaction, $A+B+C\rightarrow P$; is given by; $r=-\frac {d[A]}{dt}=K[A]^{1/2}[B]^{1/2}[C]^{1/4}$. The order of the reaction is:

  1. 1

  2. 2

  3. 1/2

  4. 5/4
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

As we know,

For a reaction, $A+B\rightarrow Product$, if rate $=K[A]^m[B]^n$, the order of reaction $=m+n$.

So here for the given reaction, order of reaction $= 1/2+1/2+1/4 = 5/4$

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

If the concentration is measured in mol $L^{-1}$ and time in minutes, the unit for the rate constant of a third order reaction is:

  1. mol $L^{-1}\, min^{-1}$
  2. $L^{2}\, mol^{-2}\, min^{-1}$
  3. $L\, mol^{-1}\, min^{-1}$
  4. $min^{-1}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

As we know,
$k\, =\, [conc]^{1-n}\, min^{-1}$
For third order reaction = $[mol\, L^{-1}]^{1-3}\, min^{-1}$
$L^2\, mol^{-2}\, min^{-2}$

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

For which of the following reactions, the units of rate constant and rate of reaction are same ?

  1. First order reaction

  2. Second order reaction

  3. Third order reaction

  4. Zero order reaction
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

For zero order,
R = k[A]
Unit of rate = mol $L^{-1}\, t^{-1}$
Unit of zero order = mol $L^{-1}\, t^{-1}$

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

If a reaction involves gaseous reactants and products, the units of its rate are:

  1. $atm$
  2. $atm$ $s$
  3. $atm$ $s^{-1}$
  4. $atm^2s^2$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

If a reaction involves gaseous reactants and products, the unit of its rate is $atm\ s^{-1}$. It represents the change in pressure (in atm units) in unit time ($1$ second).

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

The rate of certain hypothetical reaction A + B + C $\rightarrow$ Products, is given by $\displaystyle r\, =\, - \frac{dA}{dt}\, = k[A]^{1/2}[B]^{1/3}[C]^{1/4}$ The order of a reaction is given by:

  1. $1$
  2. $\displaystyle \frac{1}{2}$
  3. $2$
  4. $\displaystyle \frac{13}{12}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

$A + B + C$ $\rightarrow$ Products
$\displaystyle r\, =\, - \frac{dA}{dt}\, = k[A]^{1/2}[B]^{1/3}[C]^{1/4}$
so order is
$\displaystyle \frac{1}{2}\, +\, \frac{1}{3}\, +\, \frac{1}{4}\, =\,\frac{13}{12}$

Multiple choice chemistry chemical kinetics dependence of reaction rate on concentration of reactants order of reactions factors influencing rate of a reaction

Consider the following elementary reaction,
    $2A + B + C \rightarrow Products$.
All reactant are present in the gaseous state and reactant C is taken in excess.

What is the unit of rate constant of the reaction?

  1. $mol\, L^{-1}\, time^{-1}$
  2. $time^{-1}$
  3. $mol^{-1}\, L^{2}\, time^{-1}$
  4. $mol^{-2} L^{2} time^{-1}$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Since C is taken in excess, so its concentration does not change. So it is not taken in rate expression of the reaction.


and rate law is given by,

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

Order of the reaction $= 3$

 For the third-order reaction, the unit of the rate constant is given by -

      $= [conc.]^{1 - n} {time}^{-1}= [conc.]^{1 - 3} {time}^{-1}=\, mol^{-2} L^{2} time^{-1}$