Question

Why is boiling water an example of a physical change but iron turning into rust is a chemical change?

Answer 1

It's because in boiling water no new products are formed as they are in same quantity before being boiled..

Explanation:

But some can escape as vapour, but in a closed system you will see that there was no loose in quantity..

Iron turning into rust is as a result of oxidation which is a chemical change..

New products are formed as a result of this change..

Answer 2

Well, physical changes are LARGELY changes of state:....

Explanation:

Well, physical changes are LARGELY changes of state:....

`"Solid "rarr" Liquid"` `"; Melting"`

`"Liquid "rarr" Gas"` `"; Boiling"`

`"Gas "rarr" Solid"` `"; Deposition."`

`"Solid "rarr" Gas"` `"; Sublimation."`

And when water boils it undergoes the transition liquid to gas....and so it falls under the physical change umbrella..

On the other hand, chemical change is characterized by the formation of new substances and the making and breaking of STRONG chemical bonds....and so when iron rusts

`2Fe(s) +3/2O_2(g) rarrFe_2O_3(s)`...

...strong metallic and covalent bonds are manifestly broken, and new substances are manifestly formed, and clearly this betokens chemical change...

An undergraduate question would be to classify the dissolution of common salt in water...

`NaCl(s) stackrel(H_2O)rightleftharpoonsNa^+ + Cl^-`

Which category do you reckon?