Chemistry 12th Edition

Published by McGraw-Hill Education
ISBN 10: 0078021510
ISBN 13: 978-0-07802-151-0

Chapter 6 - Thermochemistry - Questions & Problems - Page 264: 6.45

Answer

$H_{(g)}$.

Work Step by Step

$Na_{(s)}$, $Ne_{(g)}$, $CH_{4(g)}$, $S_{8(s)}$ and $Hg_{(l)}$ are in their standard states. These elements are stable at $25^{\circ}C$ and 1 bar pressure and occur in pure form. In the standard state standard enthalpy of formation is zero. $H_{(g)}$ is not the stable standard state at $25^{\circ}C$ and 1 bar pressure. Therefore the standard state standard enthalpy of formation of $H_{(g)}$ is not equal to zero. The stable standard state of hydrogen is $H_{2(g)}$
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