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?
L A W (fact)
When proven that it
always works
THEORY
When supported
over time
HYPOTHESIS
List examples of scientific
theories and laws….
Laws
Theories
Laws
Theories
Ideal gas law: PV=nRT
Describes 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.
Theory of plate tectonics: Earth’s crust is
divided into plates that move. Explains why
earthquakes and volcanoes occur in certain
zones.
Newton’s second law of motion: F=ma
Describes the relationship between force, mass, and
acceleration.
Laws
Theories
Ideal gas law: PV=nRT
Describes 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.
Theory of plate tectonics: Earth’s crust is
divided into plates that move. Explains why
earthquakes and volcanoes occur in certain
zones.
Newton’s second law of motion: F=ma
Describes the relationship between force, mass, and
acceleration.
Brainstorm

Jot down everything you know about the
behavior and properties of gases and the gas
laws.
Boyle’s Law
7 investigations
deal with changes
in pressure as a
result of changes
in volume
New Experiments
PhysicoMechanicall,
Touching the
Spring of the Air,
and its Effects...
(1662)
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

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Herapath (1821):


Gas particle momentum is a measure of the absolute temperature of
the gas
Waterston (1843):

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
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
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)

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Included only translational particle motion
Gundzüge einer Theorie der Gase Ann. Phys. 79, 368, 500
Clausius (1857)
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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):


Boltzmann (1890s):
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Maxwell distribution: gives the proportion of molecules
having a certain velocity in a specific range
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
1662
1738
Boyle’s
Law
1802
1857
Charles’
Law
Bernoulli
Hydrodynamica
(initial ideas about
particle motion)
Clausius’
first “complete” version of
Kinetic Molecular Theory
“Modern” Kinetic Molecular Theory

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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.
L A W (fact)
When proven that it
always works
THEORY
When supported
over time
HYPOTHESIS
THEORY
HYPOTHESIS
LAW
THEORY
LAW
• Explanatory principle
• Concise, descriptive principle
• Based more on inference
• Based more on observation
• Based on lots of evidence
• Based on lots of evidence
• Can change w/ new evidence
• Can change w/ new evidence
(May Become)
HYPOTHESIS