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Current Question (ID: 8385)
Question:
$\text{Consider the following reactions:}$
$\text{(i) COCl}_2 \text{ (g)} \rightleftharpoons \text{CO (g) + Cl}_2 \text{ (g)}$
$\text{(ii) CO}_2 \text{ (g) + C (s)} \rightleftharpoons \text{2CO (g)}$
$\text{(iii) 2H}_2 \text{ (g) + CO (g)} \rightleftharpoons \text{CH}_3\text{OH (g)}$
$\text{Which reaction(s) will shift in a backward direction when the pressure is increased?}$
Options:
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1. $\text{Only (iii)}$
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2. $\text{Only (ii)}$
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3. $\text{Both (i) and (ii)}$
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4. $\text{None of the above.}$
Solution:
$\text{Hint: Use Le Chatelier's Principle}$
$\text{According to Le Chatelier's principle, when pressure is increased, a system at equilibrium will shift in the direction that reduces the pressure. This means the reaction will favor the side with fewer moles of gas.}$
$\text{Let's analyze each reaction:}$
$\text{(i) COCl}_2 \text{ (g)} \rightleftharpoons \text{CO (g) + Cl}_2 \text{ (g)}$
$\text{Left side: 1 mole of gas (COCl}_2\text{)}$
$\text{Right side: 2 moles of gas (CO and Cl}_2\text{)}$
$\text{When pressure increases, the reaction will shift to the side with fewer moles of gas to reduce pressure. Therefore, reaction (i) will shift in the backward direction (toward COCl}_2\text{).}$
$\text{(ii) CO}_2 \text{ (g) + C (s)} \rightleftharpoons \text{2CO (g)}$
$\text{Left side: 1 mole of gas (CO}_2\text{) and 1 mole of solid (C). Note that solids don't contribute to pressure.}$
$\text{Right side: 2 moles of gas (2CO)}$
$\text{When pressure increases, this reaction will also shift in the backward direction (toward CO}_2 \text{ and C) since there are fewer moles of gas on the left side.}$
$\text{(iii) 2H}_2 \text{ (g) + CO (g)} \rightleftharpoons \text{CH}_3\text{OH (g)}$
$\text{Left side: 3 moles of gas (2H}_2 \text{ and CO)}$
$\text{Right side: 1 mole of gas (CH}_3\text{OH)}$
$\text{When pressure increases, this reaction will shift in the forward direction (toward CH}_3\text{OH) since there are fewer moles of gas on the right side. It will NOT shift in the backward direction.}$
$\text{Therefore, reactions (i) and (ii) will shift in the backward direction when pressure is increased.}$
$\text{The correct answer is option 3: Both (i) and (ii).}$
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