Why is it necessary to run a blank control when using chen's test?

What is the number of moles in 15.0 g ash3?

List four observations that indicate that a chemical reaction may be taking place

Consider the following reactions. (note: (s) = solid, (l) = liquid, and (g) = gas.) mg(s) + ½o2(g) → mgo(s) + 146 kcal/mole h2(g) + ½o2(g) → h2o(g), δh = -57.82 kcal/mole what type of reaction is represented by the previous two examples?