Scitech | EXBAN-ding the truth behind the breaking of bonds

Decreasing belief in the ‘magic exothermic bond’

The field of physical chemistry is largely driven by energy: it investigates the question of where it comes from and where it goes. Fundamental physical chemistry concepts play a crucial role in many fields of science, especially biology. The formation and breakage of the chemical bonds between atoms in biological systems are at the crux of most of life’s basic functions. Despite this, the majority of students who have not taken physical chemistry courses share a common, erroneous belief: that the breaking of bonds is an exothermic process. The myth of the ‘magic bond’ – one which produces energy spontaneously when broken – is one that a group of McGill professors have been struggling to dispel for many years.

EXBAN, the Exothermic Bond Breaking Abolition Network, aims to increase awareness about this frequently misunderstood process. The group believes that overly simplified textbooks and the misleading phrasing are major contributors to students’ struggles with the concept. Any student who has ever read a basic biochemistry textbook will find abundant mentions of “energy-rich bonds,” bonds which “release free energy when broken,” and energy “liberated with the breaking of bonds.” It is not surprising, then, that many students think that when a bond is broken, energy is magically released. While it is true that the overall reaction may release energy; the initial bond breakage requires an energy input. It is the formation of the bonds in the product molecules which actually release energy. When this released energy is greater than the energy input there will be an overall release of energy – this is what is known as an exothermic reaction.

Dr. William Galley, a professor of chemistry at McGill, began to notice that many students believed this common misconception shortly after his arrival at the university in the 1970s. After noticing that a significant number of students misunderstood bond breakage year after year, he began to employ a questionnaire in his introductory physical chemistry courses to better understand where the confusion was coming from. He found that students from various backgrounds, including those who had studied general chemistry at McGill and those who had studied it at a CÉGEP, believed in this ‘magic bond.’ In 2003, Galley joined forces with Dr. Christian Hardtke – a former McGill biology professor – who, at the time, taught introductory molecular biology courses. Hardtke began to devote about thirty minutes of his class to explaining the true nature of reaction energetics. Since then, Galley noticed that the number of students who believed in the exothermic bond started to decrease. However, when Hardtke left McGill several years later, Galley found himself back at square one.

Galley continues to believe that students need to understand the chemistry behind how life, and energy, works in order to be competent in their future careers in science. He asserts that students need to have a firm grasp on fundamental concepts before they can learn more advanced material.

In order to bring awareness to his cause, Galley has presented about the misconception of bond breakage at Chemical Institute of Canada (CIC) conferences, encouraging professors to correct this mistake. He has also written about it in the Journal of Chemical Education, a widely-read publication among those who teach chemistry.

Galley believes that educators are largely to blame for the students’ misunderstandings in this area. One instructor who perpetuates the myth can affect hundreds or even thousands of students, who then must relearn a fundamental concept in a later class. And those students who don’t learn the true nature of bond breakage instead learn to rely on overly simplified books instead of their own critical analysis of the concept.

Many introductory biology and chemistry textbooks compress reaction energetics to the point where the idea of exothermic bond breakage is strongly implied, if not stated outright. In glossing over the topic, these books mislead students. This isn’t a unique phenomenon: after all, in middle school students mistakenly believe that electrons travel in concentric circular orbits, and that only compounds containing hydroxyl groups can be bases. These instances of simplifying complex concepts can help students better grasp new ideas, with the assumption that these erroneous notions will later be corrected.

But in the case of the exothermic bond, students aren’t purposely misled with the purpose of helping them understand fundamental ideas. Rather, the concept is treated as unimportant and no efforts are made to further educate students on the truth behind bond breaking. Full explanations of reaction energetics are missing from almost every introductory biochemistry textbook, and instead, ambiguous colloquial phrases such as “energy-rich bonds” are used in place of the truth. Further biology courses aren’t likely to spend time explaining endothermic bond breaking, so students will continue to believe in the ‘magic bond’ unless they take higher-level chemistry courses.

For those who do not further their studies in cell biology, or biochemistry these simplified ideas may suffice. But biochemistry is a subject that is meant to incorporate biology and chemistry. There is nothing wrong with simplifying complex subjects to make them more accessible, but doing so without making mention of the possibility that there may be more to the subject matter does a disservice to students who are actually interested in this subject.
The reaction energetics of biological processes cannot be fully understood without recognizing that bond breaking is endothermic. The energy flow within a cell is determined by a series of chemical reactions, and our cells’ ability to break down and form molecules depends on the sources of energy in metabolic pathways. Reaction energetics may remain an insignificant detail to some students but others in introductory science classes may go on to become doctors, nurses, pharmacists, and pharmacologists. One could ask: how can they understand how to fight disease if they don’t understand how the body works at a basic level?

Fortunately, though, most students have been very receptive to EXBAN. There are several student testimonials on the group’s website, many of which thank the group for encouraging them to think critically about what they learn.

Instructors and students alike can learn more about the energy changes associated with bond breakage at the EXBAN website. The hope is that instructors will see the page and make an effort to harmonize what is taught in lower level classes with what students are expected to know in their physical chemistry courses and beyond. Just like bonds themselves, the myth of the ‘magical exothermic bond’ will require more energy before it can be broken.


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