Reaction Enthalpy Calculator Dialog

This dialog appears when you click on the button from any “Reactions” tab (for a stoichiometric or kinetic reaction or fermentation); it presents an interface that allows you to estimate the reaction’s enthalpy based on each participant’s enthalpy of formation.

You can change the assumed physical state (PS) of any participant (reactant or product) in this dialog (just as you can from the Reaction Participants PS Dialog) but you cannot change the stoichiometric coefficients (in molar or mass format). You will have to exit this dialog and visit the Reaction Stoichiometry Balance Dialog (for chemical reactions) or the Bio-Reaction Stoichiometry Balance Dialog (for fermentation reactions).

You can change the assumed reference temperature where the reaction enthalpy is to be calculated and the reference component (can be any reactant or product component).

This calculator will engage each element’s enthalpy of formation at 25°C (as specified on the component’s Pure Component Properties Dialog: Physical (Constant) Tab) and assuming that the state of the component is whatever its normal boiling point dictates (if NBP is higher than 25°C then liquid; if NBP is lower than 25°C, then vapor). As such, the reaction enthalpy calculator cannot be invoked in the case that at least one reaction participant components is in the vapor phase at the enthalpy of formation reference temperature (i.e., its normal boiling point is below 25°C) and its vapor parameters have been declared to be ‘Unknown/Irrelevant’. This is because the calculation of the reaction enthalpy would require a transition from the vapor to the liquid state which is not possible, as the component is lacking enthalpy of vaporization data and ideal gas C_p data.

The standard enthalpy of reaction, H_rxn, can be calculated by summing the standard enthalpies of formation of the reactants and subtracting the value from the sum of the standard enthalpies of formation of the products, as described by the following equation.

eq. (A.33)

Notice that the program will calculate the enthalpy at the reaction enthalpy reference temperature and participant component states as specified by the user.