Since the heat of reaction is negative, why isn't the heat of reaction negative for octane, too? Is it because the heat of reaction for octane is before the reaction takes place, and hence before the release of heat? Is this the reason why octane's heat is positive, while the reaction as a whole is negative? Because it must have to do with the conservation of energy. Perhaps the reaction is the system, and octane is part of the surroundings, hence the opposite signs?
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.
Since the heat of reaction is negative, why isn't the heat of reaction negative for octane, too? Is it because the heat of reaction for octane is before the reaction takes place, and hence before the release of heat? Is this the reason why octane's heat is positive, while the reaction as a whole is negative? Because it must have to do with the conservation of energy. Perhaps the reaction is the system, and octane is part of the surroundings, hence the opposite signs?
![Using the following equation for the combustion of octane, calculate the heat of reaction for 400.0 g of
octane. The molar mass of octane is 114.33 g/mole.
2 C8H18 + 25 O2 16 CO2 + 18 H2O AH°fxn7-11018 kJ
AD19280 kJ
B) 19.28 kJ
C) 38560 kJ
D) 50400 kJ
Answer: A
BEFORE
COMBUSTION
400.05 Cotlas mol C8Hs8
110 18KJ
19,274.03131 kJ
114.33, c8Has 2mol C8H48](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fb01156c3-4f42-4f24-8d9e-b5123e3d8863%2F44028292-b0aa-40bf-8149-834a23ea21f3%2Fbbtfppp_processed.png&w=3840&q=75)
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