Is Rusting a Physical or Chemical Change? (And Why?)

Rusting is a chemical change. It involves a chemical reaction between iron and oxygen in the presence of water or moisture, resulting in the formation of iron oxide. ¹ This process alters the chemical composition of the iron, leading to the formation of a new substance with different properties.

Well, this was just a simple answer. But there are few more things to know about this topic which will make your concept super clear.

So let’s dive right into it.

Why is rusting a chemical change?

Rusting is considered a chemical change because it involves a chemical reaction between iron, oxygen, and water. It is a process known as corrosion, specifically iron corrosion. 

Here’s why rusting is classified as a chemical change:

1. Formation of new substances: When iron reacts with oxygen in the presence of water, a chemical reaction occurs, resulting in the formation of a new substance known as iron oxide, commonly referred to as rust. ² Rust is different in chemical composition and properties from the original iron.
2. Irreversibility: Rusting is typically an irreversible process. Once iron undergoes corrosion and transforms into rust, it is challenging to revert it back to its original form. This irreversible nature indicates a chemical change rather than a physical change, which can often be reversed.
3. Alteration of properties: Rust possesses different properties compared to iron. Iron is solid, strong, and malleable, whereas rust is a brittle, powdery substance. The change in physical properties indicates a chemical transformation.

In summary, rusting involves the formation of a new substance, the irreversibility of the process, energy exchange, and alterations in physical properties, all of which are characteristics of a chemical change.

Why is rusting not a physical change?

Rusting is not considered a physical change because it involves a chemical reaction between iron, oxygen, and water, resulting in the formation of a new substance called rust. Physical changes typically involve alterations in the physical state or appearance of a substance, without changing its chemical composition.

In further explanation, rusting goes beyond surface-level changes and involves the rearrangement of atoms and the formation of new chemical bonds.

When iron reacts with oxygen in the presence of water, iron atoms lose electrons and combine with oxygen and hydroxide ions to form iron(III) hydroxide, which further reacts with oxygen to form iron(III) oxide, commonly known as rust.

During this process, the iron atoms undergo a chemical transformation, resulting in a new chemical composition and different properties. Unlike physical changes, such as changes in state or shape, rusting cannot be reversed by simply reversing the conditions or physical manipulations.

Once the iron undergoes corrosion and transforms into rust, it requires chemical processes to convert it back to its original form.

To summarize, rusting is not a physical change because it involves a chemical reaction that leads to the formation of a new substance with different properties, and it cannot be reversed by physical means alone.

Further reading

Is Photosynthesis a Chemical Change?
Is Sublimation a Physical or Chemical Change?
Is Decomposition a Chemical Change?
Is Combustion a Physical or Chemical Change?
Is Condensation a Physical or Chemical Change?

1. Rusting – Redox, rusting and iron – (CCEA) – GCSE Chemistry (Single Science) Revision – CCEA – BBC Bitesize. (n.d.). BBC Bitesize. https://www.bbc.co.uk/bitesize/guides/z7rswty/revision/2
2. Foundation, C. (n.d.). CK12-Foundation. CK12-Foundation. https://flexbooks.ck12.org/cbook/ck-12-middle-school-physical-science-flexbook-2.0/section/5.16/primary/lesson/chemical-equations-ms-ps/