When dilute HCl (hydrochloric acid) is added to iron fillings, a chemical reaction takes place, resulting in the production of hydrogen gas and iron chloride. This can be explained by examining the balanced chemical equation for the reaction:

Fe (s) + 2HCl (aq) → FeCl2 (aq) + H2 (g)

Explanation:
1. Introduction:
- The reaction involves the addition of dilute hydrochloric acid (HCl) to iron (Fe) fillings.
- The iron fillings are solid (s) while hydrochloric acid is in aqueous form (aq).

2. Reaction:
- The iron fillings react with hydrochloric acid to produce iron chloride and hydrogen gas.
- The balanced chemical equation for the reaction is: Fe (s) + 2HCl (aq) → FeCl2 (aq) + H2 (g).
- In this equation, the coefficient 2 in front of HCl indicates that two moles of hydrochloric acid are required to react with one mole of iron.

3. Products:
- Iron chloride (FeCl2) is formed as an aqueous solution (aq) during the reaction. It is a compound composed of iron (Fe) and chlorine (Cl).
- Hydrogen gas (H2) is produced as a byproduct of the reaction. It is a colorless and odorless gas.

4. Explanation:
- The reaction between iron and hydrochloric acid is an example of a single displacement or substitution reaction.
- In this type of reaction, one element is displaced or substituted by another element in a compound.
- In this case, iron displaces hydrogen from hydrochloric acid to form iron chloride and hydrogen gas.
- The displacement occurs because iron is more reactive than hydrogen.

5. Significance:
- The production of hydrogen gas is one of the observable signs of the reaction.
- Hydrogen gas is highly flammable and can be used as a fuel source.
- Iron chloride, on the other hand, is a compound that has various industrial applications.

In conclusion, when dilute hydrochloric acid is added to iron fillings, a chemical reaction occurs, resulting in the formation of iron chloride and hydrogen gas. This reaction is a single displacement reaction where iron displaces hydrogen in hydrochloric acid.