Click on Download Reaction Slide Show (pdf presentation - 37 pages) for detailed information on the Reaction Module.

The Reaction module is used to calculate changes in extensive thermodynamic properties (H, G, V, S, Cp, A) for a single species, a mixture of species or for a chemical reaction. The species may be pure elements, stoichiometric compounds or ions (both plasma and aqueous ions).

For example, Fig. 2 shows the entry of the isothermal standard state reaction for the oxidation of copper:

4 Cu + O₂ = 2 Cu₂O

Note that the phases are not specified (i.e. most stable is requested). In Fig. 3 the T(K) temperature range (300 to 2000 in steps of 300) is entered and Reaction determines the most stable phases at each temperature and lists common thermodynamic values including the transition temperatures.

For example at 1200 K the stable standard state phases are Cu(s), O₂(g), Cu₂O(s), and the changes in the standard state properties are ΔHº = -332.62 kJ, ΔGº = -162.43 kJ, ΔSº = -141.83 J/mol-K, Keq = 1.176 x 106. All the common thermodynamic equations are respected, for example:

ΔGº = ΔHº - T ΔSº = - R T ln K_eq

Fig. 4 shows entry of the non-standard state reaction:

4 Cu(s, activity X) + O2(g,Po₂) = 2 Cu₂O(s)

In Fig. 5 the power of the interactive spreadsheet output format of Reaction is demonstrated. For example, in line 1 the user sets the activity of Cu(s) and the partial pressure of O₂ at standard conditions (a = X =1, P = 1) and the changes in the standard enthalpy (ΔHº = -33.54 kJ), Gibbs energy (ΔGº = -191.16 kJ) etc. are calculated at 1000 K. In line 2, with the activity of Cu(s) still set to unity (X = 1.0), the Gibbs energy change is set to zero (i.e. equilibrium) and the equilibrium oxygen pressure is calculated to be Po₂ = 1.0359 x 10-10 atm. In line 3 the equilibrium activity of Cu(s) is calculated (3.1903x10-3) when Po₂ = 1.0 atm. In the last entry (line 4) O2 with Po₂ = 10-12 atm and Cu with a(Cu(s)) =1 are at equilibrium (ΔG = 0) at the calculated temperature 897.01 K.

The Reaction module is a simple and effective teaching tool in giving students a ‘feel’ for thermochemical calculations. It is not limited to isothermal reactions and equilibrium constants. By appropriate entries you can perform heat balances, calculate adiabatic flame temperatures (by setting ΔH = 0), solve simple equilibria, determine vapor pressures, calculate aqueous solubilities, etc. The results may also be automatically displayed as graphs and stored or exported in the form of spreadsheets (for example Excel®).

For example, the enthalpy requirements to heat Al(s) from 300 K to various temperatures are calculated in Fig 6 and plotted in Fig 7. Fig. 8 illustrates a variety of calculations for the simple combustion of methane in excess oxygen. Fig 9 shows the effect of the 'VdP' term and high pressure on the graphite to diamond transition. Fig 10 involves aqueous chemistry and demonstrates a thermal balance for the leaching of zinc oxide.

Fig. 1 - Reaction Module Fig. 2 - Reaction Module - Reactants Window Cu-O2-Cu2O system. Entry of the isothermal standard state reaction for copper oxidation.. Fig. 3 - Reaction Module - Table Window Cu-O2-Cu2O system. Calculation of common thermodynamic values. Fig. 4 - Reaction Module - Reactants Window Cu-O2-Cu2O system. Entry of the isothermal non-standard state reaction for copper oxidation. Fig. 5 - Reaction Module - Table Window Cu-O2-Cu2O system. Calculation of thermodynamic values by the interactive spreadsheet format. Fig. 6 - Reaction Module - Heating Al: setting the graphical display with Figure. Fig. 7 - Reaction Module - Heating Al: a few thermodynamical considerations. Fig. 8 - Reaction Module - Combustion of methane in excess <Alpha> O2 - adiabatic reactions. Fig. 9 - Reaction Module - Effect of high pressure on the graphite to diamond transition. Fig. 10 - Reaction Module - Thermal balance for leaching of zinc oxide.