where formula_36 is a measured heat change value (corrected for all extraneous heat contributions) at data point "j", formula_37 is the amount of heat absorbed or emitted when 1 mole of the "i"th reaction product is formed and formula_38 is the actual change in the number of moles of that product at that data point.formula_39 is calculated by solving the equations of mass-balance with given values of the equilibrium constants. If the equilibrium constant values are known, the standard enthalpy change may be calculated by a linear least-squares process, otherwise a non-linear method of data-fitting must be used.