The enthalpies of formation of SnO(s) and SnO 2 (s) are -68 and -138 kcal/mol, respectively. A mixture of the two oxides contains SnO and SnO 2 in the mole ratio 3:1. If by oxidation it is changed int

Question

The enthalpies of formation of SnO(s) and SnO 2 (s) are -68 and -138 kcal/mol, respectively. A mixture of the two oxides contains SnO and SnO 2 in the mole ratio 3:1. If by oxidation it is changed into a 1:3 mole ratio mixture, how much thermal energy will be released per mole of the initial mixture?

TestHub · Accepted Answer

Take 4 mol of initial mixture: 3 SnO + 1 SnO 2 , containing 4 mol Sn. Final mixture x SnO + 3x SnO 2 with the same Sn: 4x = 4, so x = 1 (1 SnO + 3 SnO 2 ). H initial = 3(-68) + (-138) = -342 kcal. H final = (-68) + 3(-138) = -482 kcal. Heat released = 140 kcal per 4 mol = 35 kcal per mole of initial mixture. This is option (a).

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