The applicability of the Born-Oppenheimer approximation to molecule-metal surface reactions is presently a topic of intense debate. We have performed classical trajectory calculations on a prototype activated dissociation reaction, of N2 on Ru(0001), using a potential energy surface based on density functional theory. The computed reaction probabilities are in good agreement with molecular beam experiments. Comparison to previous calculations shows that the rotation of N2 and its motion along the surface affect the reactivity of N2 much more than nonadiabatic effects.