* Physical Change: A physical change alters the form or appearance of a substance but doesn't change its chemical composition.

* Chemical Change: A chemical change results in the formation of new substances with different chemical properties.

When you smell paint thinner, you are detecting volatile organic compounds (VOCs) that are evaporating from the liquid. The paint thinner itself hasn't changed chemically. It's simply releasing some of its molecules into the air.

Here's a breakdown:

1. Paint thinner is a liquid. It has a specific chemical composition.

2. The odor you smell is caused by VOCs evaporating. The paint thinner's chemical makeup hasn't changed, just its physical state (some molecules are now in the air).

3. The paint thinner itself remains mostly unchanged. It's still paint thinner, just with slightly less liquid volume due to evaporation.

In short, the odor is a physical manifestation of molecules moving from liquid to gas, not a change in the chemical composition of the paint thinner.