When you toast a marshmallow over the fire it gets golden brown or even black if you keep it on for too long. This is a chemical reaction because it cannot be reversed. Similar to bananas browning over time.
Change of Color
Before food goes bad a chemical change has to take place. That's what makes have such a foul odor. It's not always bad though like the smell coming from the oven when baking a cake.
Change of Odor
When you light a fire it burns the wood and uses it as a type of fuel. This is a chemical change and it releases heat and light.
Change of Temperature
Another form of chemical change is the formation of a solid. Like when snow or hail starts coming down or when acid is poured into mild to make solid curds of cottage cheese.
Formation of Precipitate
When dissolving an anti-acid tablet in water it produces gas bubbles. This is a chemical change taking place. Similar to when you are baking a cake and gas bubbles form in order for the cake to rise.