[en] The temperature dependence of five types of reactions of muonium atoms in aqueous solution have been measured between 2 and 92⁰C by the muonium spin rotation (MSR) technique. Results show that for an electron-transfer reduction with MnO₄^-, for an addition to π bonds in maleic acid, and for a spin-conversion reaction with Ni²⁺, the rate constants are all diffusion limited. An activation energy for diffusion of 17.5 kJ mol^-1 was found, while the A factors varied somewhat in the range approx. 10¹³ M^-1 s^-1. For these diffusion-controlled reactions there was no kinetic isotope effect when compared with H atoms, so the diffusion coefficient, even for these very small light species, is mass independent. For the abstraction reaction with formate ions, on the other hand, there is a large kinetic isotope effect and the rate constant is activation controlled. The reaction between muonium and NO₃^- was also studied and tends to exhibit a curved Arrhenius plot even over this short temperature range. Such curvature is consistent with either a contribution from quantum mechanical tunneling or alternative reaction paths