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Current Question (ID: 8396)
Question:
$\text{The value of the equilibrium constant of the reaction}$
$\text{HI(g)} \rightleftharpoons \frac{1}{2}\text{H}_2\text{(g)} + \frac{1}{2}\text{I}_2 \text{ is 8.0.}$
$\text{The equilibrium constant of the reaction}$
$\text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons \text{2HI(g) will be-}$
Options:
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1. $\frac{1}{16}$
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2. $\frac{1}{64}$
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3. $16$
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4. $\frac{1}{8}$
Solution:
$\text{Hint: Relations between Equilibrium Constants for a General Reaction and its Multiples.}$
$\text{Step 1:}$
$\text{Given,}$
$\text{HI(g)} \rightleftharpoons \frac{1}{2}\text{H}_2\text{(g)} + \frac{1}{2}\text{I}_2\text{(g)}$
$\text{K}_1 = \frac{[\text{H}_2]^{1/2}[\text{I}_2]^{1/2}}{[\text{HI}]} = 8.0$
$\text{Step 2:}$
$\text{We need to find the equilibrium constant for the following reaction:}$
$\text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons \text{2HI(g)}$
$\text{K}_2 = \frac{[\text{HI}]^2}{[\text{H}_2][\text{I}_2]}$
$\text{We notice that the second reaction is the reverse of the first reaction, but with all coefficients multiplied by 2.}$
$\text{For the reverse reaction, the equilibrium constant is the reciprocal of the original:}$
$\text{K}_{\text{reverse}} = \frac{1}{\text{K}_{\text{forward}}}$
$\text{When we multiply all coefficients in a reaction by a factor } n\text{, the equilibrium constant is raised to the power } n\text{:}$
$\text{K}_{n\times\text{coefficients}} = (\text{K}_{\text{original}})^n$
$\text{For our case, the second reaction is the reverse of the first with all coefficients doubled, so:}$
$\text{K}_2 = \frac{1}{(\text{K}_1)^2} = \frac{1}{(8.0)^2} = \frac{1}{64}$
$\text{Therefore, the equilibrium constant of the reaction H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons \text{2HI(g) is } \frac{1}{64}\text{.}$
$\text{The correct answer is option 2: }\frac{1}{64}$
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