Germain Henri Hess (1802-1850), a Swiss chemist and pioneer in the field of thermochemistry. Hess' Law states that if a chemical reaction is carried out in a series of steps, the change in enthalpy for the reaction will be equal to the sum of the enthalpy changes for the individual steps. The experiments that led to Hess’ Law were important because they wed thermodynamics and chemistry, showing that that the law of conservation of energy applied to chemical changes as well as to physical changes. In addition, these experiments suggested that chemical reactions, like physical processes, had an inherent spontaneous direction in which entropy was increased.