When iron reacts with oxygen, it forms iron oxide, or rust.

To determine how much iron oxide is formed when iron reacts with oxygen, we can use the law of conservation of mass, which states that mass is neither created nor destroyed in a chemical reaction. Therefore, the total mass of the reactants will equal the total mass of the products.

Given:
- Mass of iron = 112 g
- Mass of oxygen = 24 g

First, we find the total mass of the reactants:

\[
\text{Total mass of reactants} = \text{mass of iron} + \text{mass of oxygen} = 112 \, \text{g} + 24 \, \text{g} = 136 \, \text{g}
\]

Since all the iron and oxygen will combine to form iron oxide, the mass of iron oxide formed will be equal to the total mass of the reactants:

\[
\text{Mass of iron oxide} = 136 \, \text{g}
\]

Therefore, when 112 g of iron reacts with 24 g of oxygen, 136 g of iron oxide (rust) is formed.