Saved Bookmarks
| 1. |
Outof C and CO whichisa betterreducingagentat 983K ? |
|
Answer» Solution :Whencarbon reacts withdioxygen TOW reactions are possible: `C(s) + O_(2)(g) to CO_(2) (g)` `2C(s) + O_(2)(g) to 2CO(g)` The CO thus producedcanalso reactwith`O_(2)`to FORM `CO_(2)` . `2 CO(g) + O_(2) (g) to 2CO_(2)(g)`In the firstreaction, the volumeof `CO_(2)`produced is the sameas that of `O_(2)`pordoued is the sameas that of `O_(2)`used, therefore, `DeltaS` is very small and `Delta_(f)G^(@)` does notchangeswithtempreature. Thus, the graph of `Delta_(f)G^(@)` against T is almosthorizontal .(Fig . 6.19)  Thesecond reactionpreducestwo volumesof COforeveryone volumeof ` O _ 2`used.Thus,` DeltaS`is positiveandhence` Delta _f G ^(@) `becomesincreasinglynegativeas thetemperatureincreases.Consequenty, C, CO lineontheEllinghamdiagramslopesdownwards . Thethirdreactionproducestwo volumesof` CO_ 2`foreverythreevolumesofreactantsused.Thus, ` DeltaS` is-veandhence`Delta_ fG^(@) `becomesincreasingly+veas thetemperatureincreases. Consequentrly,CO, `CO_ 2`lineonthe Ellinghamdiagramslopesupwards. Thethreelinescrossat983 K . Belowthistemperature, FORMATIONOF` CO_ 2`fromCaswellasfromCOisenergeticallymorefavourable.Inotherwords, below 983 K ,both Cand Cocanact asreducingagentsbut sinceCOcanbemore easilyoxidisedto`CO_ 2`thanC to`CO_2`,therefore , below983 K, COisamoreeffectivereducingagentthanC. However, above983 K, COis morestableandhenceitsoxidationto` CO _ 2`isless rapidthanthatofC to` CO _ 2`. Therefore,above983 K, C isabetterreducingagentthan CO. |
|