How do different spices react to heat? I'm working on a chili recipe.  It has a bunch of spices.  I'm trying to figure out when best to add them.  People sometimes recommend "opening up" spices like cumin by toasting them or frying them in hot oil along with the onions.  OTOH, I have felt like cinnamon has much more punch-per-gram when I add it at the very end and don't cook it much/at all.  I'm sure there's a lot of chemistry involved, and different spices will behave differently when brought to different temperatures, but I haven't seen good info on it. 

So, does anyone have any information on "max temperatures" or cooking approaches with individual spices?

EDIT: I did just find this link, Indian Spices 101, which talks about it from an Indian culinary perspective.  Interesting.
I can't speak to the chemistry but I can describe the approaches I use in different spices and see if that helps. As Willem mentions in his comment, different cuisines may treat spices differently to bring out different aspects of the flavor.


Dried Herbs: typically I will add once I've begun the "watery/saucy" stage of a dish. I want these to simmer in the dish typically. Examples of these are Dried Oregano, Dried Rosemary, Dried Basil, Bay Leaves.
Fresh Herbs: typically I add these later in the cycle; many recipes will call for X tsp dried or X tbsp fresh of a particular herb. In these situations, my assumption why I prefer adding them later to the dish is that they are directly providing the flavor instead of diffusing the dried form into the sauce. I add cilantro as a finishing in both Mexican and Indian dishes. Similarly Basil is often added as a finishing ingredient.
Garlic: is a good example of multiple preparations used to bring out different aspects of the Garlic flavor. Roasting the garlic tends to mellow out the sharpness/spiciness of the garlic. This is done for some soups and often when making garlic butter for garlic bread. Raw garlic has a sharp kick that is used to flavor pestos. Sauteing garlic with onions or red peppers is a common starting point that isn't as sharp as raw garlic and not as creamy as the baked garlic.