Hot soup is tastier than cold soup. Why?

The molecules in a warm soup are more active than those in a cold soup. This means more of the flavors are more easily liberated into the air where they can be picked up by the nose and infusing the liquid of the soup itself, where it comes in contact with the taste-buds in the mouth. Some soups are served cold on purpose, such as vichyssoise, which is a potato and leek soup.