Activation volume ($\Delta V^{‡\circ }$)

The pressure derivative of the standard Gibbs energy of activation: $\Delta V^{‡\circ }=(\partial \Delta G^{‡\circ }/\partial p{)}_T$. In the corresponding rate convention, $\Delta V^{‡\circ }=-RT(\partial \ln k/\partial p{)}_T$. A negative value makes increasing pressure accelerate the reaction. Solvent reorganization can contribute as well as the intrinsic reacting geometry.