One way to obtain products from a non-spontaneous process that is exhibited in this experiment is by “coupling” two reactions. The principle of Coupled Reactions is based on a simple concept: we can use a thermodynamically favorable (spontaneous) reaction to drive an unfavorable one. One step is allowed to supply enough free energy for the other to occur. A coupled reaction is a system wherein a non-spontaneous reaction is combined with a highly spontaneous one resulting to a spontaneous overall reaction. By adding up the ΔG° values of both reactions, a negative value will result, indicating a spontaneous reaction. In the experiment, the formation of C¬¬¬¬(s) from the breakdown of CO¬¬¬2 (g)¬¬ was carried out through coupling the process with the oxidation reaction of Mg(s). CO¬2(s)¬¬¬¬ C(s) + O2(g)
2Mg(s) + O2(g) 2MgO(s)
2Mg(s) + CO2(s) C(s) + 2MgO(s)
Magnesium is a stable element and reacted violently with the liberation of much heat through combustion. The magnesium ribbon burned inside the dry ice (CO2(s)) mainly because it combined with oxygen in CO2 thus leaving elemental carbon behind. The Mg ribbon burned in air resulted to the formation of the white product (MgO) while the rest of the Magnesium ribbon that burned between the two slabs of dry ice resulted to a black product (C(s)). The Magnesium had been oxidized and the Carbon in Carbon Dioxide has been reduced to elemental Carbon.