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The Relationship between Balancing Reactions and Reaction Lifetimes: A Consideration of the Potassium–Argon Radiometric Method for Dating Minerals

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William A. Howard

Department of Chemistry and Biochemistry, University of Alaska Fairbanks, Fairbanks, AK 99775-6160

J. Chem. Educ., 2005, 82 (7), p 1094

DOI: 10.1021/ed082p1094

Publication Date (Web): July 1, 2005

Section:

History, Education, and Documentation

Abstract

Knowing the mechanism for a chemical reaction means that you can also know what the products of that reaction are, how much of each product is formed, and the kinetics of product formation. Conversely, not knowing what the products are, how much of each product is formed, or the kinetics of product formation means that the mechanism of the reaction cannot be fully known. This line of thinking, commonly taught in college chemistry courses throughout the world, applies as well to nuclear decay reactions occuring in minerals. When a geochronologist determines a mineral's age by the potassium–argon method, it is implied that the mechanism(s) by which ⁴⁰Ar came to be inside the mineral are known. Yet, geochronologists never identify and quantify the other products that must form in addition to ⁴⁰Ar. In fact, no one even knows what the other products are, in any mineral. One may argue that, because most of the products from the potassium–argon reaction are unknown, the geochronologist cannot actually know how the ⁴⁰Ar atoms came to be inside the mineral and, hence, cannot fully know the mineral's age. Formulating and critically examining such arguments can be an important part of the education of scientists.

Keywords (Audience):

Upper-Division Undergraduate

Keywords (Domain):

Inorganic Chemistry

Keywords (Pedagogy):

Problem Solving / Decision Making

Keywords (Subject):

Geochemistry

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Citing Articles

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This article has been cited by 4 ACS Journal articles (4 most recent appear below).

A Consideration of the Potassium-Argon Radiometric Method for Dating Minerals
William A. Howard
Journal of Chemical Education2006 83 (4), 546
- A Consideration of the Potassium-Argon Radiometric Method for Dating Minerals
  William A. Howard
  Journal of Chemical Education2006 83 (4), 546
  This response to Bartlet's letter has three objectives: (1) to clarify the point of contention between Bartelt and the article she is critical of; (2) to address a scientific question inspired by her letter; and (3) to comment on the importance of ...
  Abstract | Hi-Res PDF | PDF w/ Links
A Consideration of the Potassium-Argon Radiometric Method for Dating Minerals
Reed A. Howald
Journal of Chemical Education2006 83 (4), 547
- A Consideration of the Potassium-Argon Radiometric Method for Dating Minerals
  Reed A. Howald
  Journal of Chemical Education2006 83 (4), 547
  Karen Bartelt’s letter is not a fair evaluation of the William A. Howard paper. There are educational advantages of getting students involved in the scientific analysis of even controversial topics like the potassium–argon method of dating minerals.
  Abstract | Hi-Res PDF | PDF w/ Links
A Consideration of the Potassium-Argon Radiometric Method for Dating Minerals
Richard Firestone
Journal of Chemical Education2006 83 (4), 547
- A Consideration of the Potassium-Argon Radiometric Method for Dating Minerals
  Richard Firestone
  Journal of Chemical Education2006 83 (4), 547
  Karen Bartelt’s letter criticizing the paper by William Howard goes too far. This paper must be considered on its merits, not on perceived intentions, and it should be credited for teaching students to be critical in their analysis of data.
  Abstract | Hi-Res PDF | PDF w/ Links
A Consideration of the Potassium-Argon Radiometric Method for Dating Minerals
Karen E. Bartelt
Journal of Chemical Education2006 83 (4), 545
- A Consideration of the Potassium-Argon Radiometric Method for Dating Minerals
  Karen E. Bartelt
  Journal of Chemical Education2006 83 (4), 545
  William A. Howard’s recent JCE article “The Relationship between Balancing Reactions and Reaction Lifetimes: A Consideration of the Potassium–Argon Radiometric Method for Dating Minerals” is written to create confusion in his primary audience—...
  Abstract | Hi-Res PDF | PDF w/ Links