Question

The reddish brown substance formed on iron is called_____________.

Answer 1

Chemical change:

• During a chemical change, the substances undergo a chemical reaction.
• As a result of this, new substances (products) are formed which differ in their chemical composition from the original substances.
• For example When an object made of iron$\left(\mathrm{Fe}\right)$ comes in contact with moist air for some time, it undergoes a chemical change and forms iron oxide, a reddish-brown powdery substance called rust($\left(\mathrm{Fe}2{\mathrm{O}}_3\right)$
• $\underset{\mathrm{iron}}{4\mathrm{Fe}\left(\mathrm{s}\right)}+\underset{\mathrm{oxygen}\mathrm{from}\mathrm{moist}\mathrm{air}}{3{\mathrm{O}}_2\left(\mathrm{g}\right)}\stackrel{}{\to }\underset{\mathrm{rust}}{2{\mathrm{Fe}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)}$
• Iron oxide (rust) is a new substance and its properties are different from that of iron.
• Iron oxide (rust) cannot be changed back into iron, hence it is a permanent and irreversible change.

Therefore, the reddish brown substance formed on iron is called rust.