Validated speciation models and revised thermodynamic data have been used to establish the temperature dependence of the concentrations of all the main species in aqueous Cu(II)-H2SO4 and Fe(II)-Fe(III)-H2SO4 solutions in the 25-65 degrees C temperature range. Mathematical relationships have been derived for the temperature dependence of the equilibrium constants for the relevant reactions and also for the species concentrations in a well specified set of conditions. These relationships have been developed in order to use them as components of complex temperature-dependent models in hydrometallurgy, but they are also useful as stand-alone predictors of equilibrium data in the studied systems.