The spark is an effect of the chemical change, not a chemical change itself. nitron is an old, old, old, old name. I wrote nitrogen, I think, and you should too. But, perhaps if you monitor this site, another tutor may give you a clearer answer than mine seemed to be.
Also, is the white powder a chemical change? since color changing is a chemical change.
The FORMATION of the white powder is a chemical change or the production of MgO from Mg is a chemical change but white powder sitting in a beaker is not a chemical change. Do you know the definition of a chemical change? A chemical change is one in which the starting materials are changed to different products. It can be the synthesis of a new product or decomposition of an existing material. For example, when hydrogen gas reacts with oxygen gas, water is produced. We no longer have hydrogen gas and we no longer have oxygen gas. We have a NEW product, water, which is unlike either of the reacting materials. Likewise, when Mg ribbon reacts with oxygen of the air, we no longer have Mg, and we no longer have oxygen, both have been converted to MgO, a new entity. That process is a chemical change. You wanted to count the spark (the flame) as a chemical change. How would it fit the definition? You also suggested color. The color of my sofa is turquoise but its still a sofa when I finish looking at it. You wanted to count mass as a chemical change; however, if a weigh a beaker of pennies, I may find they have a mass of 55 grams BUT I still have a beaker of pennies. The pennies have not been changed into something different. I grant you that you may be able to trade those pennies for a candy bar and you might argue that you had changed pennies into a candy bar but the only thing that has happened is that the pennies were exchanged for a candy bar and someone else has the money and they still are pennies. They didn't suddenly get changed into dimes or quarters.
Any reaction you write with Mg in which the Mg is changed to something else is a chemical change. That's why\
Mg + O2 ==> MgO
Mg + N2 = Mg3N2
Mg + P ==> Mg3P2
I hope this helps.
Thanks alot! Your examples helpes me.