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Chemical reactivity is the tendency of a species to undergo a specified chemical reaction under specified conditions. A meaningful comparison identifies the reacting partner, solvent or phase, temperature, and measured outcome.

Thermodynamic favorability and reaction speed are different: a transformation may lower Gibbs free energy yet proceed slowly because its activation energy is high. A catalyst can change that barrier without changing the equilibrium constant. Reactivity therefore connects molecular electronic structure and geometry with both chemical thermodynamics and chemical kinetics.

A molecular conformation is a spatial arrangement accessible through motions such as rotations around single bonds, without changing the molecule's connectivity. Distinct conformations can have different potential energies and interconvert at different rates.

For ethane, rotation around the carbon-carbon bond connects staggered and eclipsed conformations. For cyclohexane, ring motions connect chair conformations. A drawing therefore specifies more than a molecular formula: the geometry can control steric interactions, orbital alignment, and chemical reactivity. A sufficiently high interconversion barrier can make particular conformations separately observable.