A quantitative description of the influence of salts and buffer components on the degradation of proteins is important for the shelf life of pharmaceuticals and operating life of biocatalysts but is currently lacking. By modeling observed protein deactivation as the result of competing chaotrope-dependent and ion hydration-independent processes, we develop a model to fit experimental data and describe Hofmeister effects on the deactivation of a variety of proteins in chaotropic or kosmotropic aqueous solution. We demonstrate that four parameters are required to characterize loss of function of a protein in aqueous salt solution: (i) a protein-dependent kosmotropic deactivation constant k(p), (ii) a chaotropic preexponential factor k(c), (iii) an ion hydration coefficient omega, and (iv) the B-viscosity coefficient of the salt. This model fits our experimental data on horse-liver alcohol dehydrogenase (HL-ADH), alpha-chymotrypsin, and monomeric red fluorescent protein (mRFP). We calculate the kinetic m values (m double dagger) to indicate whether the transition state of deactivation resembles the native state or the unfolded state. We find that the transition state of deactivation in a strongly chaotropic aqueous solution resembles the unfolded state (thermodynamic control) and infer that with decreasing chaotropicity the resemblance with the native state increases until at B approximate to 0 kinetic control dominates. The developed model demonstrates the importance of ion hydration effects for the explanation of Hofmeister effects on proteins and leads to an expression for a kinetic equivalent of the Wyman linkage which can be used as an alternate method for calculating m double dagger parameters in aqueous solution at any salt composition and temperature with targeted experimental effort.