 In this image, you see iron heated to a very high temperature. What kind of a change do you think this is? Is this a physical change or a chemical change? Well, let's think about it. When we are heating iron, iron is still iron right, but it has changed its temperature and possibly its shape or size. But the iron atoms have not changed their chemical properties. And the iron can still be turned back into its original form, right? Or is it in state by cooling it down? So, this seems like a physical change, because no new substance is really formed. Initially, we had a cooler iron, now we just have hotter iron. So, this is just an example of a physical change. Alright, what about this though? So, we see rusting on these locks. What kind of a change is this? Is this physical or chemical? So, turns out rusting is an example of a chemical change. When iron is exposed to moisture and oxygen for a long time, it can rust. And rust really is a reddish-brown coating that forms on the surface of iron. And it is made up of different substances than the original iron. So, this changes chemical because the iron atoms, they have reacted with oxygen and water to form a new substance, which is iron oxide. And this iron oxide has different chemical properties and cannot be turned back into pure iron by just simple physical means like heating or cooling. So, rusting is an example of a chemical change. And in fact, this change happens over a long period of time. It can happen over months and years.