Challenges in quantifying how force affects bond formation have hindered the widespread adoption of mechanochemistry. Here, parallel tip-based methods are used to determine reaction rates, activation energies, and activation volumes of force-accelerated [4+2] Diels-Alder cycloadditions between surface-immobilized anthracene and four dienophiles that differ in electronic and steric demand. The rate dependences on pressure are unexpectedly strong, and significant differences are observed between the dienophiles. Multiscale modeling demonstrates that, in proximity to a surface, mechanochemical trajectories ensue that are distinct from those observed solvothermally or under hydrostatic pressure. These results provide a  framework for anticipating how experimental geometry, molecular confinement, and directed force contribute to mechanochemical kinetics.