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 - Study Questions - Page 217i: 110



Work Step by Step

Palmitic acid combustion: $C_6H_{32}O_2(s)+13\ O_2(g)\rightarrow 6\ CO_2(g)+16\ H_2O(g)$ Enthalpy: $6\times-393.509+16\times-241.83-$ $-848.4=-5383\ kJ/mol$; $-5383\ kJ/mol\div 136.32\ g/mol=$ $-39.5\ kJ/g$ Starch combustion: $C_6H_{10}O_5(s)+6\ O_2(g)\rightarrow 6\ CO_2(g)+5\ H_2O(g)$ Enthalpy: $6\times-393.509+5\times-241.83-$ $-960=-2610\ kJ/mol$; $-2610\ kJ/mol\div 162.14\ g/mol=$ $-16.10\ kJ/g$ Per peanut: $0.73\ g\times (49/100\times-39.5\ kJ/g+21/100\times-16.10\ kJ/g)=-16.60\ kJ$ Heat required: $250\ mL\times 1\ g/mL\times 4.184\ J/g.K\times (100-25)\ K=78.45\ kJ$ Peanuts required: $78.45/16.60=4.72$ 5 peanuts required.
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