Chemistry and Chemical Reactivity (9th Edition)

Published by Cengage Learning
ISBN 10: 1133949649
ISBN 13: 978-1-13394-964-0

Chapter 5 Principles of Chemical Reactivity: Energy and Chemical Reactions - 5-7 Enthalpy Calculations - Case Study - Questions: 1

Answer

Gasoline provides more energy per mol and per gram.

Work Step by Step

Enthalpies of formation (kJ/mol): $C_6H_6O(l): -277.0, C_8H_18(l): -250.1, CO_2(g): -393.5, H_2O(l): -285.8$ Ethanol: $C_6H_6O+7\ O_2\rightarrow 6\ CO_2+3\ H_2O$ $\Delta H_c= 6\times-393.5+4\times-285.8+277.0=-3227.2\ kJ/mol$ $-3227.2\ kJ/mol\div 94.11\ g/mol=-34.29\ kJ/g$ Octane: $C_8H_{18}+25/2\ O_2\rightarrow 8\ CO_2+9\ H_2O$ $\Delta H_c= 8\times-393.5+9\times-285.8+250.1=-5470.1\ kJ/mol$ $-5470.1\ kJ/mol\div 114.23\ g/mol=-47.89\ kJ/g$ Gasoline provides more energy per mol and pet gram.
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