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Conservation of Mass

Mass of products equals mass of the reactants.

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A Balanced Account

A Balanced Account


Credit: Liam Skoda
Source: https://commons.wikimedia.org/wiki/File:Dexamphetamine_sulfate_5_mg_tablets.jpg
License: CC BY-NC 3.0

“Over $500,000 in Drugs Missing” – this was a headline about a hospital where an employee had taken large amounts of narcotics over a period of months. Nobody in the hospital knew of the theft because no inventory had been taken. The drugs had come in and been logged according to protocol, but there was no tracking of where the drugs went and how they were used. One-half the equation was there, but it had not been balanced.

News You Can Use

  • Balancing equations is considered a chore by most chemistry students. The process usually focuses on “getting the right number”, and neglects the idea that we cannot create or destroy matter. All chemical reactions merely rearrange the atoms that are present. A different order is achieved, a different set of molecules comes out of the mix, but you always have the same number of atoms of each type at the end that you had at the beginning.
  • The hospital in the example above has committed a significant error. The drugs that were stolen were expensive, they were controlled substances, and they were purchased for treatment of patients. There was no accountability being shown and no way of knowing if anything was disappearing. Drugs do not just “vanish” – someone takes them, either to give to a patient or to steal for their own use and/or profit.
  • When a surgical procedure take place, a careful count is kept of every instrument and item that is used. For patient safety, the inventory at the end of the operation must match the list at the beginning. Failure to follow this procedure can result in harm to the patient and extra expense (second surgery, lawsuits) to the hospital. What you had at the beginning needs to agree completely with what you have at the end.
  • There is an exception to the rule, however (there is always one somewhere). Matter and energy are interconvertible. Under most ordinary circumstances this is not a big issue. However, if we are dealing with nuclear reactions, the issue becomes significant. In fission and fusion processes, there are slight differences between the masses of the reactants and the masses of the products. This difference is seen as a release of energy in keeping with the famous Einstein equation \begin{align*}E = mc^2 \end{align*}E=mc2 which states the relationship between energy \begin{align*}(E)\end{align*}(E) and mass \begin{align*}(m)\end{align*}(m). This energy then becomes an important component of nuclear processes.
  • Credit: Ferdinand Schmutzer
    Source: http://en.wikipedia.org/wiki/File:Einstein_1921_by_F_Schmutzer.jpg
    License: CC BY-NC 3.0

    Albert Einstein in 1921. His famous equation has been dubbed "The world's most famous equation" [Figure2]


  • Watch a video about conservation of mass at the link below: https://www.youtube.com/watch?v=J5hM1DxaPLw

Show What You Know

Use the links below to learn more about matter and energy. Then answer the following questions.

  1. What does the first law of thermodynamics tell us?
  2. List two reasons it is important to balance your bank account.
  3. What are problems associated with leaving a sponge or other item inside a patient?
  4. How has the Mayo Clinic addressed this problem?

Image Attributions

  1. [1]^ Credit: Liam Skoda; Source: https://commons.wikimedia.org/wiki/File:Dexamphetamine_sulfate_5_mg_tablets.jpg; License: CC BY-NC 3.0
  2. [2]^ Credit: Ferdinand Schmutzer; Source: http://en.wikipedia.org/wiki/File:Einstein_1921_by_F_Schmutzer.jpg; License: CC BY-NC 3.0

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