Consider the following reversible reaction:
[tex]\[ 2 \text{H}_2\text{O} (g) \leftrightharpoons 2 \text{H}_2(g) + \text{O}_2(g) \][/tex]

What is the equilibrium constant expression for the given system?

A. [tex]\[ K_{\text{eop}} = \frac{[\text{H}_2\text{O}]}{[\text{H}_2][\text{O}_2]} \][/tex]

B. [tex]\[ K_{S O} = \frac{[\text{H}_2\text{O}]^2}{[\text{H}_2]^2[\text{O}_2]} \][/tex]

C. [tex]\[ K_{\infty 0} = \frac{[\text{H}_2]^2[\text{O}_2]}{[\text{H}_2\text{O}]} \][/tex]

D. [tex]\[ K_{e Q} = \frac{[\text{H}_2]^2[\text{O}_2]}{[\text{H}_2\text{O}]^2} \][/tex]



Answer :

To identify the correct equilibrium constant expression for the given reaction:

[tex]\[ 2 H_2O(g) \leftrightharpoons 2 H_2(g) + O_2(g) \][/tex]

we need to use the general form of the equilibrium constant expression for a reversible reaction:

For a generic reaction of the form:

[tex]\[ aA + bB \leftrightharpoons cC + dD \][/tex]

the equilibrium constant expression (\( K_\text{eq} \)) is given by:

[tex]\[ K_\text{eq} = \frac{[C]^c [D]^d}{[A]^a [B]^b} \][/tex]

Here, \( [A] \), \( [B] \), \( [C] \), and \( [D] \) represent the molar concentrations of the reactants and products, and \( a \), \( b \), \( c \), and \( d \) are their respective stoichiometric coefficients.

Applying this to our given reaction:

[tex]\[ 2 H_2O(g) \leftrightharpoons 2 H_2(g) + O_2(g) \][/tex]

we can identify the following:
- \( [H_2O] \) with a coefficient of 2 on the reactant side
- \( [H_2] \) with a coefficient of 2 on the product side
- \( [O_2] \) with a coefficient of 1 on the product side

Thus, the equilibrium constant expression (\( K_\text{eq} \)) for this reaction is:

[tex]\[ K_\text{eq} = \frac{[H_2]^2 [O_2]}{[H_2O]^2} \][/tex]

Comparing this with the given multiple choices:

1. \( K_{\text {eop }}=\frac{\left[ H _2 O \right]}{\left[ H _2\right]\left[ O _2\right]} \)
2. \( K_{S O}=\frac{\left[ H _2 O \right]^2}{\left[ H _2\right]^2\left[ O _2\right]} \)
3. \( K_{\infty 0}=\frac{\left[ H _2\right]^2\left[ O _2\right]}{\left[ H _2 O \right]} \)
4. \( K_{e Q}=\frac{\left[ H _2\right]^2\left[ O _2\right]}{\left[ H _2 O \right]^2} \)

The correct equilibrium constant expression is:

[tex]\[ K_{e Q}=\frac{\left[ H _2\right]^2\left[ O _2\right]}{\left[ H _2 O \right]^2} \][/tex]

Therefore, the correct choice is [tex]\( K_{e Q} \)[/tex].

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