= Solution
\b[The negative <activation volume> means the transition state occupies less partial molar volume than the two separated reactants.] Pressure therefore favours reaching it and increases the forward rate, consistent with a compact associative <cycloaddition> in which new bonds begin to form.
The magnitude, about $25\ \mathrm{cm^3\,mol^{-1}}$, is molecular in scale. It includes packing and solvent reorganization as well as intrinsic bond-length changes, so it should not be interpreted as a simple geometric volume carved out of two rigid molecular surfaces.
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