[A. Peters]

Hey, I’m fairly new to the field of chemistry and I am currently creating a product that requires a sustained heat of around 100*c for around 3-5 minutes. Could I get any advice on what chemicals would create that sort of reaction and the quantity of each that would produce the intended result?

[Corribus]

This isn't how temperature or chemistry works. There are no magic ingredients that deliver a target temperature for a sustained period of time. Reactions do give off (or absorb) heat, but the temperature of the resulting system, to say nothing of its time dependence, depends on the physical properties (heat capacity, etc.) of the medium in which the chemicals are placed, the volume and shape of the system, the amount and concentration of ingredients, and a variety of engineering parameters such as the mixing rate, rate of ingredient addition, insulation properties of the system, and so forth. Just not possible to answer this question I'm afraid.

[A. Peters]

Thank you, Corribus, for the correction. I honestly have no idea on how chemicals work, but I’ll figure out my problem with something other than chemistry.

[Enthalpy]

A compound that reacts with water strongly enough to let water boil would achieve a stable temperature around 100°C. Most such compounds are badly dangerous, but maybe iron powder, spoiled with copper, would be safe enough - or maybe not.

Let water drip on the reactive compound, so more vapour pressure slows down the water flow, which stabilizes the reaction speed?

As far as possible, I'd boil water by other means, like electricity, to achieve a stable temperature. Or melt a paraffin chosen for adequate temperature, and use it as a heat source while it solidifies. Some alloys too melt around 100°C.