When the oxide of a generic metal, M, is heated at 25 °C, only a negligible amou

Question

When the oxide of a generic metal, M, is heated at 25 °C, only a negligible amount of M(s) is produced. If this reaction is coupled to the oxidation of graphite by oxygen to form carbon dioxide, it becomes spontaneous a. What is the complete chemical equation for the coupled process? b. Calculate AGu for the coupled process. Consider the non-coupled conversion of titanium(IV) oxide to titanium metal in the above equation. If Arnis +944 kJ mot-1 and Son is +1 85.3 J mol-1 K-1, at what temperature will this reaction become spontaneous? c.

Explanation / Answer

MO2(s)<----------->M(s)+ O2, deltaGo= 290 Kj/mole (1)

fpr the combustion of graphite, C(s)+O2(g)<--------->CO2(g), deltaG= -394.39 Kj/mole (2)

Addition of Eq.1 and Eq.2 gives MO2(s)+C <------->M(s)+CO2(g), deltaG=290-394.39 =-104.39 Kj/mole

the reaction is spontaneous because if deltaG is -ve

2. TiO2(s)<-------->Ti(s)+ O2(g), deltaH= 944 Kj/mole= 944*1000 j/mole and deltaS= 185.3 J/mole

let us first calculate the temperature at which deltaG= deltaH-T*deltaS=0

T= deltaH/deltaS= 944*1000/(185.3)=5094 K

at temperatures above 5094K, deltaG will be -ve which makes the process spontaneous.

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