A variable temperature scanning tunneling microscope was used to directly observe the thermally induced rotation of a single acetylene molecule between two equivalent orientations on Cu(001) above 68 K. Measurements of the rotation rate as a function of temperature yielded an energy barrier of 169 +/- 3 meV and a preexponential factor of 10(11.8 +/- 0.2) s(-1). Thermal diffusion of individual acetylene molecules was monitored above 178 K by single molecule tracking. A diffusion barrier of 0.53 +/- 0.01 eV and a preexponential factor of 10(13.6 +/- 0.2) s(-1) were determined by measuring the hopping rate as a function of temperature.