Abstract: A self-heating chemical system using one or more primary components for exothermic reactions (such as calcium oxide), one or more porous components that can serve as a heat sink and conductor of heat as well as under going chemical transformations that release heat (zeolite), a weak acid (citric acid) for sustained modulation of temperature and pH. Exothermic reactions, mixing of some chemicals, sorption of certain chemicals, phase changes in chemicals, and dissolution of some chemicals in solvents release heat during these operations. The rate of heat generation coupled with mass and energy transfer rates to or from system(s) allows modulation of the temperature of systems. The modulation can be further enhanced by controlled release and availability of some of the components.