SiO2(s) + 4 HF(aq) → SiF4(g) + 2 H2O(l) ∆Horxn = 4.60 kJ ∆Hof, kJ/mol: ??? -320.1 -1.62 x 106 –285.8 a) If the standard enthalpy of reaction for the dissolution of silica in aqueous HF is 4.60 kJ, what is the standard enthalpy of formation of SiO2g) in kilojoules/mole? b) If the Gibbs’ Free energy for this reaction at 25.0oC is -125372.5295 Joules and the standard entropy is 475.93 J/K, above what temperature will this reaction run in the forward direction?
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
SiO2(s) + 4 HF(aq) → SiF4(g) + 2 H2O(l) ∆Horxn = 4.60 kJ ∆Hof, kJ/mol: ??? -320.1 -1.62 x 106 –285.8
a) If the standard enthalpy of reaction for the dissolution of silica in aqueous HF is 4.60 kJ, what is the
standard enthalpy of formation of SiO2g) in kilojoules/mole?
b) If the Gibbs’ Free energy for this reaction at 25.0oC is -125372.5295 Joules and the standard entropy
is 475.93 J/K, above what temperature will this reaction run in the forward direction?
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