34. Without doing any calculations, determine the sign of ? S sys and ? S surr f

Question

34. Without doing any calculations, determine the sign of ?Ssys and ?Ssurr for each chemical reaction. In addition, predict under what temperatures (all temperatures, low temperatures, or high temperatures), if any, the reaction will be spontaneous.

a.    2 CO(g) + O2(g) ? 2 CO2(g)              ?Hrxn= ? 566.0 kJ

b.    2 NO2(g) ? 2 NO(g) + O2(g)                       ?Hrxn= + 113.1 kJ

c.     2 H2(g) + O2(g) ? 2 H2O(g)              ?Hrxn= ? 483.6 kJ

d.    CO2(g) ? C(s) + O2(g)                     ?Hrxn= + 393.5 kJ

Explanation / Answer

2 CO(g) + O2(g) ? 2 CO2(g) dS sys < 0 dS sur > 0

2 NO2(g) ? 2 NO(g) + O2(g) dS sys > 0 dS sur < 0

2 H2(g) + O2(g) ? 2 H2O(g) dS sys < 0  dS sur > 0

CO2(g) ? C(s) + O2(g)  dS sys slightly > 0 dS sur < 0

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