This communication introduces an FRET-based simple and efficient method for monitoring kinetics and thermodynamics of organic reactions and describes its application to studies on the initial catalyst-substrate association step in the enyne metathesis catalyzed by a Grubbs Ru complex to probe the reaction initiation on the alkyne versus the alkene. The kinetic and thermodynamic parameters of alkene and alkyne with the first generation Grubbs Ru complex, determined by the time-dependent fluorescence quenching of the dye-conjugated substrate by the Ru catalyst, strongly support the dominance of the reaction initiation on alkene over alkyne in the reaction both kinetically and thermodynamically.