Lifting of nodes by disorder in extended-$s$ state superconductors: application to ferropnictides

We show, using a simple model, how ordinary disorder can gap an extended-$s$ ($A_{1g}$) symmetry superconducting state with nodes. The concommitant crossover of thermodynamic properties, particularly the $T$-dependence of the superfluid density, from pure power law behavior to an activated one is exhibited. We discuss applications of this scenario to experiments on the ferropnictide superconductors.