Here's how to write and balance the equation for the reaction of iron metal with chlorine gas to form solid iron chloride:

1. Write the unbalanced equation:

Fe(s) + Cl₂(g) → FeCl₃(s)

* Fe(s): Iron metal (solid)

* Cl₂(g): Chlorine gas (gaseous)

* FeCl₃(s): Iron chloride (solid)

2. Balance the equation:

* Iron (Fe): There is one Fe atom on each side, so it's balanced.

* Chlorine (Cl): There are two Cl atoms on the left and three on the right. To balance, we need to adjust the coefficients:

* Place a 2 in front of FeCl₃: Fe(s) + Cl₂(g) → 2FeCl₃(s)

* Now we have six Cl atoms on the right.

* Place a 3 in front of Cl₂: Fe(s) + 3Cl₂(g) → 2FeCl₃(s)

The balanced equation is:

Fe(s) + 3Cl₂(g) → 2FeCl₃(s)