If you like us, please share us on social media.
The latest UCD Hyperlibrary newsletter is now complete, check it out.

GeoWiki.png
ChemWiki: The Dynamic Chemistry E-textbook > Development Details > Approaches > Demos > Additional Demos > The Effect of Temperature on the NO2/N2O4 Equilibrium

MindTouch
Copyright (c) 2006-2014 MindTouch Inc.
http://mindtouch.com

This file and accompanying files are licensed under the MindTouch Master Subscription Agreement (MSA).

At any time, you shall not, directly or indirectly: (i) sublicense, resell, rent, lease, distribute, market, commercialize or otherwise transfer rights or usage to: (a) the Software, (b) any modified version or derivative work of the Software created by you or for you, or (c) MindTouch Open Source (which includes all non-supported versions of MindTouch-developed software), for any purpose including timesharing or service bureau purposes; (ii) remove or alter any copyright, trademark or proprietary notice in the Software; (iii) transfer, use or export the Software in violation of any applicable laws or regulations of any government or governmental agency; (iv) use or run on any of your hardware, or have deployed for use, any production version of MindTouch Open Source; (v) use any of the Support Services, Error corrections, Updates or Upgrades, for the MindTouch Open Source software or for any Server for which Support Services are not then purchased as provided hereunder; or (vi) reverse engineer, decompile or modify any encrypted or encoded portion of the Software.

A complete copy of the MSA is available at http://www.mindtouch.com/msa

The Effect of Temperature on the NO2/N2O4 Equilibrium

 

Chemical Concept Demonstrated

  • Temperature's effect on equilibrium

Demonstration

Four glass tubes are sealed with NO2 gas.
  1. The first tube is placed in a hot water bath.
  2. The second is placed in ice-water.
  3. The third is placed in a flask filled with dry-ice/acetone slush.
  4. The fourth is placed in liquid nitrogen.

Compare the glass tubes.

tempno2.gif

Observations

NO2 is brown and N2O4 is colorless.  The intensity of the brown color decreases as the temperature decreases.   Therefore, a decrease in temperature yields and increase in N2O4.   Equilibrium is shifted to the N2O4 side upon a decrease in temperature.


Explanation (including important chemical equations)

2 NO2 (g) <=> N2O4 (g)

The standard enthalpy (delta H° = -57.2 kJ) and the entropy (delta S° = -175.83 kJ) of reaction can be calculated from the follow standard-state enthalpies of formation and standard-state entropies.

Compound delta H°(kJ/mol) delta S° (J/mol-K)
NO2 33.18 240.06
N2O4 9.16 304.29

We can then invoke the assumption that the temperature dependence of delta H° for this reaction is small to estimate the equilibrium constant at various temperatures.

Temperature delta G° (kJ) Kp
100 °C 8.4 0.066
0 °C -9.2 58
-78 °C -22.9 1.3 x 106
-196 °C -43.6 3.7 x 1029

Contributors

 

You must to post a comment.
Last Modified
10:30, 2 Oct 2013

Tags

Classifications

(not set)
(not set)

Creative Commons License Unless otherwise noted, content in the UC Davis ChemWiki is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Permissions beyond the scope of this license may be available at copyright@ucdavis.edu. Questions and concerns can be directed toward Prof. Delmar Larsen (dlarsen@ucdavis.edu), Founder and Director. Terms of Use