Out of C and CO, which is a better reducing agent at 673 K?
At 673 K, the value of `triangleG_(CO,CO_2)` is less than that of `triangleG_(("C,CO"))` Therefore, CO can be oxidised more easily to CO2 than C to CO. Hence, CO is a better reducing ag ent than C at 673 K.
This can be explained thermodynamically, taking entropy and free energy changes into account.
`C(s) + O_2(g) -> CO_2(g)`
`2C(s) + O_2(g) -> 2CO (g)`
Case i: Volume of CO2 produced = Volume of O2 used.
`:.triangleS` is very small and `triangleG` does not change with temperature.
:.Plot of `triangleG` Vs T is almost hrizontal
Case ii: Volume of CO produced = 2 x Volume of O2 used
`:.triangleS` is positive and hence `triangleG` beccomes increasingly negative as the temperature increases.
:.Plot of `triangle ""^@G` Vs T slopes downwards.
As can be seen from ΔG° Vs T plot (Ellingham diagram), lines for the reactions, C ——–> C02 and C ——–> CO cross at 983 K. Below 983 K, the reaction (a) is energetically more favourable but above 673 K, reaction (b) is favourable and preferred. Thus, below 673 K both C and CO can act as a reducing agent but since CO can be more easily oxidised to C02 than C to C02 , therefore, below 673 K, CO is more effective reducing agent than carbon