The kinetics of the addition of hydrogen fluoride to vinyl fluoride have been measured in the vapor phase at temperatures of 100 and 150 °C and under pressures of 170, 308, and 446 N/m2. The rate equation was found to be a typical second order expression, −dx/dt = k[CHF=CH2] [HF]. The energy of activation was calculated to be 17 ± 2 kcal/mol, and the frequency factor, logA(l/mol s) was 6 ± 1. Based on reaction data from the literature, equilibrium constants and a value for ΔH298were calculated. For this reaction, ΔH298is about −12 kcal/mol.