exothermically

adverb1

1. •
   In an exothermic manner

   • Aldrichimica Acta Volume 30 No 4 (pdf) from Sigma-Aldrich The fused cyclobutenomaleimide is much more reactive than Smith’s diene; it reacts with cyclopentadiene exothermically at room temperature to yield the extended isomer as the major cycloaddition product.