We compare here recent results of molecular beam investigations of the initial probability of trapping-mediated C-H and C-D bond cleavage of C2H6, C2D6, C3H8, and C3D8 on Ir(110) at low beam translational energy and surface temperatures, T-S, from 85 to 800 K. Each of these systems is highly reactive at low T-S and displays decreasing reactivity with increasing T-S. Measurements of the initial probability of trapping-mediated chemisorption for both ethane and propane reveal an isotope effect, which we attribute to zero-point energy differences, with the perhydrido-species exhibiting greater reactivity at a given T-S. A difference in activation energies for desorption vs reaction (C-D bond cleavage) for C2D6 has been found to be E(d)-E(r)=1.8+/-0.3 kcal/mol, cf. E(d)-E(r)=2.2 kcal/mol for C-H bond cleavage of C2H6. For the trapping-mediated dissociative chemisorption of propane on Ir(110), E(d)-E(r)=4.2 kcal/mol for C-H bond cleavage of C3H8, and E(d)-E(r)=3.2 kcal/mol for C-D bond cleavage of C3D8. A quantitative analysis of the initial probability of trapping-mediated dissociative chemisorption of ethane and propane on Ir(110), within the context of a classical kinetic model of barrier crossing from the physically adsorbed state to the dissociatively chemisorbed state, provides the most reasonable description of the observed adsorption behavior.