Chemistry: The Central Science (13th Edition)

Published by Prentice Hall
ISBN 10: 0321910419
ISBN 13: 978-0-32191-041-7

Chapter 5 - Thermochemistry - Exercises - Page 208: 5.76

Answer

$\Delta H^o_f : CaC_2(s) = -60.7kJ$

Work Step by Step

$CaC_2(s) + 2H_2O(l) --> Ca(OH)_2(s) + C_2H_2(g)$ $\Delta H^o = -127.2kJ$ $\Delta H^o_f : H_2O(l) = -285.83 kJ/mol$ $\Delta H^o_f : Ca(OH)_2(s) = -986.2 kJ/mol$ $\Delta H^o_f : C_2H_2(g) = 226.7 kJ/mol$ $\Delta H^o_f : CaC_2(s) = x$ $-127.2 = [-986.2 +(226.7)] - [x + 2*(-285.83)]$ $-127.2 = -759.5 - [x - 571.66]$ $-127.2 +759.5= -x + 571.66 $ $632.3 = -x + 571.66$ $60.7 = -x$ $x = -60.7 kJ$
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