<P> Hess 's law is now understood as an expression of the principle of conservation of energy , also expressed in the first law of thermodynamics , and the fact that the enthalpy of a chemical process is independent of the path taken from the initial to the final state ( i.e. enthalpy is a state function ) . Reaction enthalpy changes can be determined by calorimetry for many reactions . The values are usually stated for processes with the same initial and final temperatures and pressures , although the conditions can vary during the reaction . Hess 's law can be used to determine the overall energy required for a chemical reaction , when it can be divided into synthetic steps that are individually easier to characterize . This affords the compilation of standard enthalpies of formation , that may be used as a basis to design complex syntheses . </P>
<P> Hess 's law is now understood as an expression of the principle of conservation of energy , also expressed in the first law of thermodynamics , and the fact that the enthalpy of a chemical process is independent of the path taken from the initial to the final state ( i.e. enthalpy is a state function ) . Reaction enthalpy changes can be determined by calorimetry for many reactions . The values are usually stated for processes with the same initial and final temperatures and pressures , although the conditions can vary during the reaction . Hess 's law can be used to determine the overall energy required for a chemical reaction , when it can be divided into synthetic steps that are individually easier to characterize . This affords the compilation of standard enthalpies of formation , that may be used as a basis to design complex syntheses . </P>
applications of hess 's law of constant heat summation
applications of hess 's law of constant heat summation
to determine the overall energy required for a chemical reaction
to determine the overall energy required for a chemical reaction