## Standard reaction enthalpies

Evelyn L 1H
Posts: 67
Joined: Fri Sep 29, 2017 7:05 am

### Standard reaction enthalpies

I am confused about how to calculate the standard reaction enthalpies. For example, in 8.63, part a asks to calculate the standard reaction enthalpy for the final stage in the production of nitric acid. 3NO2(g)+H2O(l) --> 2HNO3(aq) + NO(g).
What are the steps to finding the answer?

Connor Kelligrew 2D
Posts: 39
Joined: Fri Sep 29, 2017 7:07 am

### Re: Standard reaction enthalpies

For this question, you can use the standard enthalpies of formation from Appendix 2A to calculate the standard reaction enthalpy, which is one of the methods to calculating a standard reaction enthalpy.
Imagine that to carry out the reaction we convert the reactants into the elements in their most stable form, then from those elements we form the products. I would suggest looking at Figure 8.31 on page 295 of the textbook to visualize it. This line of thinking gives us this equation:

$\Delta H^{\circ}=\Sigma n\Delta H^{\circ}_{f}(products)-\Sigma n\Delta H^{\circ}_{f}(reactants)$

So in this problem you would look up the standard enthalpies of formation for $NO(g)$, $HNO_{3}(aq)$, $H_{2}O(l)$, and $NO_{2}$ from Appendix 2A and use the equation above.
Hope this helps!

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