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## AP®︎/College Chemistry

### Course: AP®︎/College Chemistry>Unit 6

Lesson 6: Hess's law

# Hess's law

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## Problem

The table below contains information about four different reactions, labeled W, X, Y, and Z.
$\text{Reaction}$$\text{Equation}$$\begin{array}{rl}& \mathrm{\Delta }H\mathrm{°}\\ & \left({\text{kJ/mol}}_{rxn}\right)\end{array}$
W$\mathrm{N}{\phantom{A}}_{2}\left(g\right)+3\phantom{\rule{0.167em}{0ex}}\mathrm{H}{\phantom{A}}_{2}\left(g\right)\to 2\phantom{\rule{0.167em}{0ex}}\mathrm{NH}{\phantom{A}}_{3}\left(g\right)$$-92$
X$2\phantom{\rule{0.167em}{0ex}}\mathrm{H}{\phantom{A}}_{2}\left(g\right)+\mathrm{O}{\phantom{A}}_{2}\left(g\right)\to 2\phantom{\rule{0.167em}{0ex}}\mathrm{H}{\phantom{A}}_{2}\mathrm{O}\left(l\right)$$-572$
Y$\mathrm{N}{\phantom{A}}_{2}\left(g\right)+2\phantom{\rule{0.167em}{0ex}}\mathrm{O}{\phantom{A}}_{2}\left(g\right)\to 2\phantom{\rule{0.167em}{0ex}}\mathrm{NO}{\phantom{A}}_{2}\left(g\right)$$66$
Z$2\phantom{\rule{0.167em}{0ex}}\mathrm{NH}{\phantom{A}}_{3}\left(g\right)+4\phantom{\rule{0.167em}{0ex}}\mathrm{H}{\phantom{A}}_{2}\mathrm{O}\left(l\right)\to 2\phantom{\rule{0.167em}{0ex}}\mathrm{NO}{\phantom{A}}_{2}\left(g\right)+7\phantom{\rule{0.167em}{0ex}}\mathrm{H}{\phantom{A}}_{2}\left(g\right)$$?$
Using the information above, determine the value of ${\mathrm{\Delta }H\mathrm{°}}_{\phantom{\rule{-0.4em}{0ex}}rxn}$ for reaction Z.
${\text{kJ/mol}}_{rxn}$