Multi-layer reaction mixtures that includes exothermic generating particles having a water soluble coating encasing a portion of the particles, a volatile component and, optionally, a buffer, an aqueous solution or both. At least two layers of the reaction mixture contain exothermic generating particles and at least one layer of the reaction mixture contains a portion of the exothermic generating particles suspended in a gel that includes the water soluble coating. These multi-layer reaction mixtures are especially suited to generate heat in a controllable manner. In one such controlled reaction, the reaction components are mixed together and the reaction mixture increases in temperature to a Set Temperature within a predetermined time, and the mixture remains at the Set Temperature for a longer period of time. In this manner, volatile components can be controllably released to the surrounding environment. The volatile components can be, for example, a perfume, a fragrance, an insect repellent, a fumigant, a disinfectant, a bactericide, an insecticide, a pesticide, a germicide, an acaricide, a sterilizer, a deodorizer, a fogging agent and mixtures of these. Apparatuses and methods that use these multi-layer reaction mixtures are also disclosed.