Is it possible to have a chemical change without a physical change?

Chemical or physical change?

• I need to determine which is a chemical change & which is a physical change: tanning of your skin by the sun (I said physical) sap dripping from a pine tree (I said physical) recovery of turpentine from pine sap (I said chemical) mixing turpentine with paint to "thin" it (I said chemical) formation of a skin rash due to contact with turpentine (I said physical) My instructor looked it over & said that several are wrong & to re-think carefully. I'm still lost.

• Answer:

  Here's the key. If it's a chemical change, a new substance that was not there before is produced. Mixing turpentine with paint does involve chemicals, but there is no chemical reaction since no new substance is produced. After you mix them, all that is present is turpentine and paint, just like before. Therefore it is a physical change. Tanning of your skin by the sun involves the production of a new substance - the dark substance that causes the tan color. Therefore it is a chemical change.