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Current Question (ID: 8394)
Question:
$\text{The equilibrium reaction that doesn't have equal values for K}_C \text{ and K}_P \text{ is:}$
Options:
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1. $\text{2NO(g)} \rightleftharpoons \text{N}_2\text{(g)} + \text{O}_2\text{(g)}$
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2. $\text{SO}_2\text{(g)} + \text{NO}_2\text{(g)} \rightleftharpoons \text{SO}_3\text{(g)} + \text{NO(g)}$
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3. $\text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons \text{2HI(g)}$
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4. $\text{2C(s)} + \text{O}_2\text{(g)} \rightleftharpoons \text{2CO}_2\text{(g)}$
Solution:
$\text{HINT: Use K}_P = \text{K}_C(\text{RT})^{\Delta n}$
$\text{The relationship between K}_P \text{ and K}_C \text{ for gas phase reactions is given by:}$
$\text{K}_P = \text{K}_C(\text{RT})^{\Delta n}$
$\text{where } \Delta n = n_P - n_R \text{ (difference between moles of gaseous products and gaseous reactants)}$
$\text{If } \Delta n = 0 \text{, then K}_P = \text{K}_C$
$\text{Let's analyze each reaction:}$
$\text{1. 2NO(g)} \rightleftharpoons \text{N}_2\text{(g)} + \text{O}_2\text{(g)}$
$n_P = 2 \text{ moles of gas (N}_2 \text{ and O}_2\text{)}$
$n_R = 2 \text{ moles of gas (2NO)}$
$\Delta n = n_P - n_R = 2 - 2 = 0$
$\text{Therefore, K}_P = \text{K}_C$
$\text{2. SO}_2\text{(g)} + \text{NO}_2\text{(g)} \rightleftharpoons \text{SO}_3\text{(g)} + \text{NO(g)}$
$n_P = 2 \text{ moles of gas (SO}_3 \text{ and NO)}$
$n_R = 2 \text{ moles of gas (SO}_2 \text{ and NO}_2\text{)}$
$\Delta n = n_P - n_R = 2 - 2 = 0$
$\text{Therefore, K}_P = \text{K}_C$
$\text{3. H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons \text{2HI(g)}$
$n_P = 2 \text{ moles of gas (2HI)}$
$n_R = 2 \text{ moles of gas (H}_2 \text{ and I}_2\text{)}$
$\Delta n = n_P - n_R = 2 - 2 = 0$
$\text{Therefore, K}_P = \text{K}_C$
$\text{4. 2C(s)} + \text{O}_2\text{(g)} \rightleftharpoons \text{2CO}_2\text{(g)}$
$\text{Note: Solids like C(s) do not contribute to the gas phase equilibrium and are not counted in } n_P \text{ or } n_R$
$n_P = 2 \text{ moles of gas (2CO}_2\text{)}$
$n_R = 1 \text{ mole of gas (O}_2\text{)}$
$\Delta n = n_P - n_R = 2 - 1 = 1$
$\text{Since } \Delta n \neq 0, \text{ K}_P = \text{K}_C(\text{RT})^1 = \text{K}_C(\text{RT})$
$\text{Therefore, K}_P \neq \text{K}_C$
$\text{The correct answer is option 4: 2C(s)} + \text{O}_2\text{(g)} \rightleftharpoons \text{2CO}_2\text{(g)}$
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