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?

Chemistry: Principles and Reactions
8th Edition
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Publisher:William L. Masterton, Cecile N. Hurley
Chapter8: Thermochemistry
Section: Chapter Questions
Problem 58QAP: Consider the following reaction in the vessel described in Question 57. A(g)+B(g)C(s)For this...
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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
Transcribed Image Text: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
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