Illumination of nanoparticles causes “photothermal heating”, where the particles heat up faster than they diffuse heat into the local environment, creating a temperature gradient between the particle and the bulk system. When used to drive chemical reactions, it’s an example of how simple spatial differences in reaction set-up can alter the macroscale behavior of systems. In the presented work, I have explored photothermal heating in solution as well as in the gas phase to perform high-temperature reactions that normally require that the bulk system be heated. The first is a radical polymerization, where we chose the thermal decomposition of benzoyl peroxide as our target reaction. We demonstrated that this reaction could be done without heating the bulk system. We also saw that the unique reaction geometry of photothermal heating resulted in morphological differences in the resulting polymer. The second reaction explored was the heterogeneous catalyst conversion of carbon dioxide to methane on nickel. Using nickel nanoparticles and light as both the catalysts and heat source, we were able to perform these reactions well below the usual bulk temperatures required, and below even what is used for supported photothermal catalysts. Finally, we extended our exploration of spatial systems to two other systems and used finite element modeling to complement reaction and system design.