Re: Why does cooking oil stain paper?

Thanks for the question, Jeanne.  

There are several answers for your question about why the oil stained your 
paper.  Some answers are fairly easy to understand, other are much more 
difficult.  I’ll stick to an easier explanation.  

The oil stained the paper because the molecules in the oil and the 
molecules in the paper were attracted to each other.  It can be said that 
the oil and the paper reached a more favorable thermodynamic state when 
they were together, compared to the when they were apart.  Thermodynamics 
is a complicated topic that I won’t get into any more here.  

It is fairly easy to see when two substances are not attracted to each 
other, for example when you try to mix oil and water, the two liquids 
remain separated.  On the other hand, when two substances are attracted to 
each other, they will bond together, often making a stain.  

If we understand this we can use it to our advantage, and we do every 
day.  The same basic principle that stained your paper with oil is used to 
print newspapers and magazines.