3. A bonus for using H2O(l), CO2(g), N2(g), NaCl(s) as reactants. These compounds are characterized by strongly nega ve enthalpy of forma on (Table ). As such, conversion of these molecules is thermodynamically challenging. Students are rewarded with 300 points for using each of these chemicals as reactants to complete the level task. Note that if any of these chemicals appear as reactants in the task, the bonus is not awarded. 4. A bonus for synthesis of elements in their standard states, H2(g), Cl2(g), Na(s), Fe(s). The enthalpy of forma on of an element in its standard state is 0 kJ mol -1 (Table ). Therefore, according to Eq. 2, synthesis of elements in the standard states from their compounds in most cases is an endothermic process (unless the standard enthalpy of forma on of such a compound is posi ve, see below). Consider, for example, dissocia on of two moles of H2O(l) into two moles of H2(g) and one mole of O2(g). ΔH 0 of this reac on is 571.66 kJ. Overall, when elements in their standard states appear as reac on products, this increases ΔG of the reac on (Eq. 1). To support the player's crea ve thinking, which allows not only comple ng the task, but at the same me to produce valuable industrial commodi es, 500 points are granted for synthesis of each of these chemicals. Note that if any of these elements are included in the task, the bonus is not awarded.