Chemistry Help. :)

Pre-College Issues High School Life
1

<p>Calculate the enthalpy change for the following reaction:</p>

<p>NO (g) + 1/2 O2 (g) -> NO2 (g)</p>

<p>Um, how do you do it with only one equation?</p>

2

<p>You look up the enthalpy of formation values in a table (there should be one in your textbook).</p>

3

<p>I did that, then do you add the enthalpy of formation values or what?</p>

4

<p>Change all of the number of mole to whole numbers.</p>

<p>2NO (g) + O2 (g) -> 2NO2 (g)</p>

<p>1.Find enthalpy of 2 moles of NO2. (Multiply value in book by 2, because the book probably gives the value for one mole)
2.Find enthalpy of 2 moles of NO (Multiply value in book by 2, because the book probably gives the value for one mole) and add enthalpy of 1 mole of O2 (Number from the book) to that.</p>

<p>Step 1- Step 2= Change in enthalpy</p>

5

<p>But isn’t that the same as enthalpy of formation? I thought they were two different things ( enthalpy of formation & enthalpy change). In my book, they separated into two different sections and from the enthalpy change, they used this Hess law alternative, which required 3 different equations given. </p>

<p>BUt thanks for making chemistry a lot simpler now (:</p>

6

<p>For Hess’ Law you need more than one equation given.
I’m pretty sure that is how you find change in enthalpy. Here is the formula.
<a href=“http://www.chem.purdue.edu/gchelp/howtosolveit/Thermodynamics/ThermoArt/Hess’sLawEquation.JPG[/url]”>http://www.chem.purdue.edu/gchelp/howtosolveit/Thermodynamics/ThermoArt/Hess’sLawEquation.JPG&lt;/a&gt;&lt;/p&gt;