For the reaction,`Fe(s) + S(s) rarr FeS(s)` the expression for equilibrium constant is

Options

A. `[FeS]/([S][Fe])`
B. `[Fe][S]/[FeS]`
C. `[Fe][S][FeS]`
D. None of these

Explanation

To find the expression for the equilibrium constant (K) for the reaction:

\[ \text{Fe(s)} + \text{S(s)} \rightleftharpoons \text{FeS(s)} \]

we follow these steps:

### Step 1: Write the general expression for the equilibrium constant (K)

The equilibrium constant expression is given by the formula:

\[ K = \frac{[\text{Products}]^{\text{stoichiometric coefficients}}}{[\text{Reactants}]^{\text{stoichiometric coefficients}}} \]

### Step 2: Identify the states of the reactants and products

In this reaction:
- Iron (Fe) is a solid.
- Sulfur (S) is a solid.
- Iron sulfide (FeS) is also a solid.

### Step 3: Consider the activity of solids in the equilibrium expression

For pure solids and liquids, their activity is considered to be 1. This means they do not appear in the equilibrium constant expression because their concentrations do not change during the reaction.

### Step 4: Write the equilibrium expression

Since all species in this reaction are solids, we do not include them in the equilibrium expression. Therefore, the expression for K becomes:

\[ K = \frac{1}{1} = 1 \]

### Step 5: Conclusion

The equilibrium constant K for the reaction is:

\[ K = 1 \]