Question

Out of C and CO, which is a better reducing agent at 673 K?

Answer 1

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.

Answer 2

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