Advanced Chemistry Theory - Questions and Answers

explanatory Essay
1613 words
1613 words

2. What was phlogiston? Based on what theoretical and experimental bases did Lavoisier reject it?

According to Bowler’s Making Modern Science, A Historical Survey, the theory of phlogiston was first stated by Johann Joachim Becher in 1667. In 1703, Georg Ernst Stahl, a professor of medicine and chemistry at Halle, proposed a variant of the theory in which he renamed Becher’s terra pinguis to phlogiston theory and it was in this form that the theory had it influence.

Phlogiston was a fire-like substance without color, odor, taste or mass that every combustible substance was in part composed of, and it was released during combustion (Bowler 56). A substance rich in phlogiston was said to be phlogisticated and once they were burned, they became dephlogisticated and back to their true form, the calx (residual substance in form of fine powder). In general, substances that burned in air were said to be phlogisticated. After trying various experiments of combustion of substances in enclosed space, it became clear that combustion ceased once in an enclosed space. This was evidence enough that air was only capable of absorbing a certain amount of phlogiston, and once air became entirely phlogisticated, it would no longer support combustion, nor could it support life of any kind since its purpose in the respiration process was to remove phlogiston from the body; thus, a calx would never be formed. In conclusion, according to the phlogiston theory, phlogiston’s role in combustion is opposite to the role of oxygen in combustion.

The phlogiston theory and the use of phlogiston in the vocabulary of many chemists remained dominant until French chemist Antoinne-Laurent Lavoisier disproved it with his caloric theory of combustion (Bowler 56). In his theory, Lavoisier showed that combustion requires a gaseous substance that has weight and that its weight can be measured. In his experiments with phosphorous and sulfur, both of which burned readily in air, Lavoisier showed that they both gained weight by combining with air. Using lead calx, Lavoisier was also able to capture a large amount of air that according to phlogiston theory was liberated when the calx was heated. These results hadn’t been explained by phlogiston theory. Even though Lavoisier had come to a realization that combustion involved air, he was still puzzled by the exact composition of air, which was not understood then. It was until 1774 when Lavoisier met with the English natural philosopher and phlogistonist Joseph Priestly, who had experimented with a mercury calx and collected a gas, which supported the burning of a candle and the respiration process of a rat (Bowler 63-66).

In this essay, the author

  • Explains that the theory of phlogiston was first stated by johann joachim becher in 1667 and georg ernst stahl's terra pinguis in 1703.
  • Explains that phlogiston is a fire-like substance without color, odor, taste or mass that every combustible substance was in part composed of, and it was released during combustion.
  • Explains how lavoisier disproved phlogiston theory with his caloric theory of combustion.
  • Explains that lavoisier repeated priestley's experiments with mercury and other metal calces, and eventually concluded that air was not a simple substance.
  • Explains that rene descartes' mechanical philosophy of corpuscularism discusses reality and change in terms of particles and their motion.
  • Explains that dalton's atomic theory is a theory of the structure and behavior of atoms.
  • Compares dalton's atomic theory with corpuscularism in that it changed the focus of chemical atoms from shape and interparticle forces to the consideration of relative weights.
  • Explains descartes' concept of mind/soul duality, which allowed for an independent realm of existence for thought, soul, and most importantly, god.
  • Explains that dalton's atomic theory employed two concepts developed by lavoisier. engineering and technology had begun to influence many philosophical innovations regarding the composition of matter.
  • Explains that lavoisier's work as a chemist mainly dealt with the study of combustion and renamed it eminently respirable.
  • Explains that lavoisier noticed that although oxygen combined with many other substances, it never behaved as a combination of others. he suggested that oxygen must be an element based on ancient greek philosophers.
  • Explains that lavoisier produced the first table of elements, which contained elements that he included in hope that further research could succeed in decomposing them. he believed that the earth substances were combinations of metals with oxygen.
  • Explains that john dalton gathered the experimental works of various natural philosophers to summarize the practical evidence on the composition of matter.
  • Explains that dalton's third postulate of the atomic theory states that atoms are the basic units of chemical changes involved in chemical reactions.
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