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Theories, Laws, and Hypotheses: Gas Laws and Kinetic Molecular Theory

Theories, Laws, and Hypotheses: Gas Laws and Kinetic Molecular Theory. Define the Terms and Draw the Relationship. Theory Law Hypothesis. How are these concepts related to each other?. Theories. Hypotheses. Laws. When supported over time. L A W (fact). When proven that it always works.

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Theories, Laws, and Hypotheses: Gas Laws and Kinetic Molecular Theory

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  1. Theories, Laws, and Hypotheses:Gas Laws and Kinetic Molecular Theory

  2. Define the Terms and Draw the Relationship • Theory • Law • Hypothesis

  3. How are these concepts related to each other? Theories Hypotheses Laws

  4. When supported over time L A W (fact) When proven that it always works THEORY HYPOTHESIS

  5. List examples of scientific theories and laws…. Laws Theories

  6. Laws Theories

  7. Laws Theories

  8. Brainstorm • Jot down everything you know about the behavior and properties of gases and the gas laws.

  9. New Experiments Physico-Mechanicall, Touching the Spring of the Air, and its Effects... (1662) Boyle’s Law 7 investigations deal with changes in pressure as a result of changes in volume

  10. Boyle’s Law: 1662

  11. Charles’ Law • The Expansion of Gases by Heat. In Annales de Chimie 43, 137 (1802) • First published by Gay-Lussac who attributed it to unpublished work of Charles’ in 1780s. Image retrieved from: http://www.freshney.org/ptonline/data/biography/jlgl.htm

  12. Kinetic Molecular Theory (Early Ideas about Molecular Motion) • Bernoulli (1738): Hydrodynamica • Gases consist of great numbers of molecules moving in all directions • Impact on a surface causes gas pressure • Heat is the kinetic energy of their motion • Herapath (1821): • Gas particle momentum is a measure of the absolute temperature of the gas • Waterston (1843): • Gas pressure is a function of the number of molecules per unit volume, molecular mass, and molecular mean-squared velocity • Published posthumously (1892) as “On the physics of media that are composed of free and perfectly elastic molecules in a state of motion" • Both Herapath and Waterston failed peer review when attempting to get their ideas published by the Royal Society of London

  13. Kinetic Molecular Theory • Krönig (1850) • Included only translational particle motion • Gundzüge einer Theorie der GaseAnn. Phys.79, 368, 500 • Clausius (1857) • Included translational, rotational, and vibrational particle motion • The size of a particle is negligibly small relative to its container • Changes in particle motion due to collisions are infinitesimal relative to time between successive collisions. • The influence of the molecular forces must be infinitesimal. • Heat is the average kinetic energy of molecules. • Published: "Über die bewegende Kraft der Wärme" ("On the Moving Force of Heat and the Laws of Heat which may be Deduced Therefrom”, Annalen der Physik 100, 353-380

  14. Kinetic Molecular Theory • Additions, Clarifications, and Modifications by: • Maxwell (1859): • Maxwell distribution: gives the proportion of molecules having a certain velocity in a specific range • Boltzmann (1890s): • Associated the kinetic energy of particles with their degrees of freedom • Described distribution of particle speeds in gases • Einstein (1905) and Smoluchowski (1906) • Brownian Motion – evidence for the existance of atoms and molecules

  15. Timeline of Gas Laws and KMT Boyle’s Law Charles’ Law Bernoulli Hydrodynamica (initial ideas about particle motion) Clausius’ first “complete” version of Kinetic Molecular Theory

  16. “Modern” Kinetic Molecular Theory • Gases consist of very small particles in constant, random motion. • Gas particles are perfectly spherical in shape and elastic in nature. • Gas particles move rapidly and constantly collide with each other and the walls of the container in perfectly elastic collisions. • The volume of individual gas particles is negligible relative to the volume of the container . • Interactions among molecules are negligible, except during collisions. • The time during collision of molecule with the container's wall is negligible as comparable to the time between successive collisions. • The average kinetic energy of the gas particles depends only on the temperature of the system.

  17. Scientific Hypothesis: • A proposed answer to a research question • A tentative explanation for an observation or phenomena that can be tested through experimentation.

  18. Scientific Theory: A general principle supported by a substantial body of evidence offered to provide an explanation of observed facts and as a basis for future discussion or investigation. Lincoln, Boxshall, and Clark (1990) Scientific Law: A scientific law is a description of a natural relationship or principle, often expressed in mathematical terms.

  19. When supported over time L A W (fact) When proven that it always works THEORY HYPOTHESIS

  20. THEORY LAW HYPOTHESIS

  21. THEORY L A W • Explanatory principle • Based more on inference • Based on lots of evidence • Can change w/ new evidence • Concise, descriptive principle • Based more on observation • Based on lots of evidence • Can change w/ new evidence (May Become) HYPOTHESIS

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