Which of these three reactions is the most endothermic reaction? Check off correct answer C(s) + O2(g) → CO2(g) ΔH = -393.5 kJ/mol S(s) + O2(g) → SO2(g) ΔH = -296.8 kJ/mol C(s) + 2 S(s) → CS2(l) ΔH = 87.9 kJ/mol
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.
Which of these three reactions is the most endothermic reaction? Check off correct answer
C(s) + O2(g) → CO2(g) ΔH = -393.5 kJ/mol
S(s) + O2(g) → SO2(g) ΔH = -296.8 kJ/mol
C(s) + 2 S(s) → CS2(l) ΔH = 87.9 kJ/mol
According to sign convention, if sign of enthalpy change is negative, the reaction is said to be exothermic.
If, sign of enthalpy change is positive, the reaction is said to be endothermic.
Here, in first two reactions, sign of enthalpy change is negative. This means that these two reactions are exothermic.
In the third reaction, the sign of enthalpy change is positive. Hence, only third reaction is endothermic.
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