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

ChemWiki: The Dynamic Chemistry E-textbook > Development Details > Approaches > Demos > Additional Demos > Limiting Reagents

Copyright (c) 2006-2014 MindTouch Inc.

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

Limiting Reagents

Chemical Concepts Demonstrated

  • Limiting
  • Excess reagents


  • A round-bottom flask is filled with O2 and sealed with a rubber stopper holding a deflagrating spoon..
  • The deflagrating spoon is filled with red phosphorus, ignited, and plunged into the oxygen filled flask.
  • A magnesium strip is ignited by the burner.


After a few moments in the flask, the red phosphorus will stop burning but a small amount will still be present on the deflagrating spoon. The magnesium strip will burn brightly until there is none remaining in the tongs.

Explanations (including important equations)

P4 (s) + 5 O2 (g) --> 4 P4O10 (s)

According to the balanced equation, if the spoon holds 2.0 g of phosporus, it would take 2.6 g of O2 to consume all of the phosphorus in the reaction.  At 25°C and 1 atm, 2.6 g of Ois slightly less than 2 L in volume. The flask can only hold 1 L of O2.  There is not enough oxygen within the flask to burn all of the phosphorus present.  Therefore oxygen is the limiting reagent.  However, the magnesium strip is burned in an open room with a large excess of oxgyen.  In this case, the magnesium ribbon is the limiting reagent.



You must to post a comment.
Last modified
10:29, 2 Oct 2013



(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