`2.1g` of `Fe ` combines with `S` evolving `3.77KJ` . The heat of formation of `FeS` in `KJ//mol` is

Options

A. `-3.77`
B. `-1.79`
C. `-100.5`
D. None of these

Explanation

To find the heat of formation of FeS in kJ/mol, we can follow these steps:

### Step 1: Determine the number of moles of iron (Fe)
Given that the mass of iron (Fe) is 2.1 g and the molar mass of iron is 56 g/mol, we can calculate the number of moles of iron.

\[ \text{Number of moles of Fe} = \frac{\text{mass of Fe}}{\text{molar mass of Fe}} = \frac{2.1 \, \text{g}}{56 \, \text{g/mol}} = 0.0375 \, \text{mol} \]

### Step 2: Relate the heat evolved to the moles of Fe
The heat evolved when 2.1 g of Fe reacts with sulfur is given as 3.77 kJ. We need to find the heat evolved per mole of Fe.

\[ \text{Heat evolved per mole of Fe} = \frac{\text{Total heat evolved}}{\text{Number of moles of Fe}} = \frac{3.77 \, \text{kJ}}{0.0375 \, \text{mol}} = 100.5 \, \text{kJ/mol} \]

### Step 3: Determine the heat of formation of FeS
Since the reaction is exothermic (heat is evolved), the heat of formation will be negative. Therefore, the heat of formation of FeS is:

\[ \Delta H_f (\text{FeS}) = -100.5 \, \text{kJ/mol} \]

### Final Answer
The heat of formation of FeS is \(-100.5 \, \text{kJ/mol}\).

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