MCQ
The equilibrium constant $K_{c}$ at $298\, \mathrm{~K}$ for the reaction  $\mathrm{A}+\mathrm{B} \rightleftharpoons \mathrm{C}+\mathrm{D}$  is $100 .$ Starting with an equimolar solution with concentrations of $\mathrm{A}, \mathrm{B}, \mathrm{C}$ and $\mathrm{D}$ all equal to $1\, \mathrm{M}$, the equilibrium concentration of $D$ is $.......\times 10^{-2}$ M. (Nearest integer)
  • A
    $18$
  • $182$
  • C
    $45$
  • D
    $18200$

Answer

Correct option: B.
$182$
b
$\mathrm{A}+\mathrm{B} \rightleftharpoons \mathrm{C}+\mathrm{D}: \mathrm{K}_{\mathrm{eq}}=100$

$1 \mathrm{M}\quad 1 \mathrm{M} \quad 1 \mathrm{M} \quad1 \mathrm{M}$

First check direction of reversible reaction.

Since $\mathrm{Q}_{\mathrm{c}}=\frac{[\mathrm{C}][\mathrm{D}]}{[\mathrm{A}][\mathrm{B}]}=1<\mathrm{K}_{\mathrm{eq} .} \Rightarrow$ reaction will move in forward direction to attain equilibrium state.

$\Rightarrow \mathrm{A}+\mathrm{B} \rightleftharpoons \mathrm{C}+\mathrm{D}: \mathrm{K}_{\mathrm{eq}}=100$

$to \quad 1\quad 1\quad\quad 1\quad 1$

$\mathrm{t}_{\text {eq. }} \, 1-\mathrm{x} \, 1-\mathrm{x} \, 1+\mathrm{x} \, 1+\mathrm{x}$

Now $: \mathrm{K}_{\mathrm{eq}}=100=\frac{(1+\mathrm{x})(1+\mathrm{x})}{(1-\mathrm{x})(1-\mathrm{x})}$

$\Rightarrow 100=\left(\frac{1+x}{1-x}\right)^{2}$

$(i)$ $10=\left(\frac{1+\mathrm{x}}{1-\mathrm{x}}\right)$

$\Rightarrow 10-10 \mathrm{x}=1+\mathrm{x}$

$\Rightarrow 11 \mathrm{x}=9$

$\Rightarrow \mathrm{x}=\frac{9}{11}$

$(ii)$ $-10=\frac{1+\mathrm{x}}{1-\mathrm{x}}$

$\Rightarrow-10+10 \mathrm{x}=1+\mathrm{x}$

$\Rightarrow-9 x=-11$

$\Rightarrow x=\frac{11}{9}$

$\rightarrow$ $'x'$ cannot be more than one, therefore not valid. therefore equation concretion of $(D)=1+x$

$=1+\frac{9}{11}=\frac{20}{11}$

$=1.8181=181.81 \times 10^{-2}$

$\simeq 182 \times 10^{-2}$

Need a full question paper?

Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.

Start Generating Free