Introduction:
When dilute hydrochloric acid (HCl) is added to a mixture of iron filings and sulfur powder, a chemical reaction takes place. This reaction involves the formation of hydrogen gas and iron(II) sulfide.

Explanation:
1. Chemical Equation:
The reaction can be represented by the following balanced chemical equation:

Fe (s) + S (s) + 2HCl (aq) → FeS (s) + 2H2 (g) + Cl2 (g)

This equation shows that iron (Fe) reacts with sulfur (S) in the presence of hydrochloric acid (HCl) to produce iron(II) sulfide (FeS), hydrogen gas (H2), and chlorine gas (Cl2).

2. Reaction Steps:
The reaction occurs as follows:

Step 1: Iron Filings and Sulfur Powder
The iron filings and sulfur powder are initially present as a mixture.

Step 2: Hydrochloric Acid (HCl)
When dilute hydrochloric acid (HCl) is added to the mixture, it acts as a catalyst to initiate the reaction.

Step 3: Formation of Iron(II) Sulfide (FeS)
The iron (Fe) reacts with the sulfur (S) to form iron(II) sulfide (FeS). This is a black solid that precipitates out of the reaction mixture.

Step 4: Release of Hydrogen Gas (H2)
As the reaction proceeds, hydrogen gas (H2) is released. This is observed as the formation of gas bubbles in the mixture.

Step 5: Generation of Chlorine Gas (Cl2)
In the presence of hydrochloric acid (HCl), chlorine gas (Cl2) is also produced. However, this gas is not usually observed in the reaction mixture as it escapes into the atmosphere.

3. Overall Observations:
When dilute hydrochloric acid is added to the mixture of iron filings and sulfur powder, the following observations can be made:

- The mixture starts to react, and gas bubbles are formed.
- A black solid, iron(II) sulfide, is formed and settles at the bottom of the reaction container.
- The reaction mixture may become warm due to the release of energy during the reaction.
- If the reaction is carried out in an open container, a pungent smell of chlorine gas may be observed.

Conclusion:
In summary, when dilute hydrochloric acid is added to a mixture of iron filings and sulfur powder, a reaction occurs resulting in the formation of iron(II) sulfide, hydrogen gas, and chlorine gas. This reaction is a classic example of a displacement reaction, where the more reactive metal (iron) displaces the less reactive non-metal (sulfur) from its compound.