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?

HYPOTHESIS

THEORY

L A W (fact)

When proven that it always works

When supported over time

List examples of scientific theories and laws….

Laws Theories

Laws TheoriesIdeal gas law: PV=nRTDescribes the relationship between pressure, volume, moles, and temperature of a gas.

Kinetic molecular theory: Matter consists of tiny particles in constant motion, whose speed is proportional to the absolute temperature. Explains gas laws.

Law of conservation of matter: First clearly stated by 18th century chemist Antoine Lavoisier, this law describes that in a closed system, matter is neither created or destroyed.

 Atomic theory: All matter is composed of elements made from indestructible particles called atoms. Explains why matter is conserved in chemical reactions.

 Law of superposition: Describes the general principle that in undeformed layers of rock, the oldest rock will be at the bottom.

 Theory of evolution by natural selection: Competition for limited resources results in differential reproductive success. Only species best adapted to their environment survive and pass on hereditable traits. Explains the phenomenon of evolution, the fossil record, and the diversity of species on Earth.

 Newton’s second law of motion: F=maDescribes the relationship between force, mass, and acceleration.

 Theory of plate tectonics: Earth’s crust is divided into plates that move. Explains why earthquakes and volcanoes occur in certain zones.

Laws TheoriesIdeal gas law: PV=nRTDescribes the relationship between pressure, volume, moles, and temperature of a gas.

Kinetic molecular theory: Matter consists of tiny particles in constant motion, whose speed is proportional to the absolute temperature. Explains gas laws.

Law of conservation of matter: First clearly stated by 18th century chemist Antoine Lavoisier, this law describes that in a closed system, matter is neither created or destroyed.

 Atomic theory: All matter is composed of elements made from indestructible particles called atoms. Explains why matter is conserved in chemical reactions.

 Law of superposition: Describes the general principle that in undeformed layers of rock, the oldest rock will be at the bottom.

 Theory of evolution by natural selection: Competition for limited resources results in differential reproductive success. Only species best adapted to their environment survive and pass on hereditable traits. Explains the phenomenon of evolution, the fossil record, and the diversity of species on Earth.

 Newton’s second law of motion: F=maDescribes the relationship between force, mass, and acceleration.

 Theory of plate tectonics: Earth’s crust is divided into plates that move. Explains why earthquakes and volcanoes occur in certain zones.

Brainstorm

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

Boyle’s Law

New Experiments Physico-Mechanicall, Touching the Spring of the Air, and its Effects... (1662)

7 investigations deal with changes in pressure as a result of changes in volume

Boyle’s Law: 1662

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

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

Kinetic Molecular Theory Krönig (1850)

Included only translational particle motion Gundzüge einer Theorie der Gase Ann. 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

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

Timeline of Gas Laws and KMT

Boyle’s Law

Charles’Law

Clausius’ first “complete” version of Kinetic Molecular Theory

BernoulliHydrodynamica

(initial ideas about particle motion)

“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.

Scientific Hypothesis:

1. A proposed answer to a research question

2. A tentative explanation for an observation or phenomena that can be tested through experimentation.

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.

HYPOTHESIS

THEORY

L A W (fact)

When proven that it always works

When supported over time

HYPOTHESIS

THEORY LAW

HYPOTHESIS

THEORY L A W

• Concise, descriptive principle

• Based more on observation

• Based on lots of evidence

• Can change w/ new evidence

• Explanatory principle

• Based more on inference

• Based on lots of evidence

• Can change w/ new evidence

(May Become)