Need reactants for a rocket
Put some potassium nitrate $\ce{KNO3}$ plus powdered charcoal and sulfur in a mortar. Wet it carefully and grind the whole until you get a black homogeneous paste. Let it dry overnight in the mortar. The obtained black gun powder may be detached from the mortar with a wooden spoon. It is a safe rocket fuel. The proportions of the powders are defined by stoichiometry. They must allow the chemical reaction : $$\ce{2 KNO3 + 3 C + S -&gt;  K2S + 3 CO2 + N2}$$
I have done it many times with my students. It's a good exercice of stoichiometry. Never had an accident ! And remember : Never ! Never grind dry powders ! Grind as wet powders as possible ! In case of doubt add more water ! Pastes are even a better choice for grinding purposes !