Chemistry 101 - Section HSolids, Liquids, and Especially

Gases• This presentation was created by

Professor Carl H. SnyderChemistry DepartmentUniversity of MiamiCoral Gables, FL 33124CSnyder@miami.edu

• Copyright 2003 by Carl H. Snyder, University of Miami. All rights reserved.

Chapter 12 - Solids, Liquids, and Especially Gases

Solids, Liquids, and Gases

• Solids - maintain their own volumes and shapes

• Liquids - maintain their own volumes but take the shapes of their containers

• Gases - maintain neither their own volumes nor shapes, but take both the volumes and shapes of their containers.

Why Solids Melt, Liquids Boil• When we heat a substance, we add energy to

its chemical particles.• This energy makes their particles move,

vibrate, rotate, etc., faster … in every way.

Melting Point

• Melting - Solid to liquid

• Freezing - Liquid to solid

Boiling Point

• Boiling - Liquid to gas throughout the entire mass of the liquid.

• Evaporation - Liquid to gas only at the surface• Condensation - Gas to liquid

Evaporation

• Evaporation occurs when molecules with high translational energies escape from the surface of the liquid.

• Evaporation can occur at temperatures far below the boiling point

Sublimation

• The disappearance of snow at temperatures too cold for melting to occur takes place through sublimation.

The Gas We Live In

The Composition of Dry Air

• Dry air is roughly 80% N2, 20% O2, and traces of other gases.

Atmospheric Pressure• The total mass of all the

atmosphere above any give point on or above the earth’s surface produces the atmospheric pressure at that point.

Measuring Atmospheric Pressure

• The barometer, an instrument for measuring atmospheric pressure

• Invented by Evangelista Torricelli

• 1643

The Kinetic-Molecular Theory

• What happens when you pump up a tire -- and much more -- is explained by the kinetic-molecular theory of gases.

• Kinetic (moving) molecular (molecules) = moving molecules.

The Basis of The Kinetic-Molecular Theory

• All gases are composed of atoms or molecules that are in constant motion, richocheting off each other and off walls like billiard balls.

• The higher the temperature, the faster the atoms or moleucles move.

The Cast of Characters

• Each of these scientists contributed to our understanding of the behavior of gases.

Robert Boyle

A Statement of Boyle’s Law

Illustrations of Boyle’s Law

• Double the pressure on a fixed quantity of gas held at constant temperature, and its volume decreases to half.

Boyle’s Law and The Kinetic-Molecular Theory of Gases

• As we decrease the volume of a constant quantity of gas molecules (kept at constant temperature), the moving molecules hit the sides of their container more often.

• This results in a higher pressure.

Jacques Alexandre Cesar Charles

• Q: But . . . what value of temperature shall we use?

• A: The Kelvin temperature.

William Thomson, Lord Kelvin• William Thomson,

Lord Kelvin, gave us the Kelvin temperature scale.

• The Kelvin temperature scale begins at absolute zero and move upward in degrees the same size as those of the Celsius scale.

Charles’ Law and The Kinetic-Molecular Theory of Gases

• As we decrease the temperature, the gas molecules move with less energy.

• If we keep the pressure constant, the volume of the gas decreases.

Can the Volume of a Gas Drop to Zero?

• No, because the gas laws apply strictly only to ideal gases.

• A real gas will condense to a liquid before it reaches absolute zero.

Combining Boyle’s Law and and Charles’ Law

• Combining Boyle’s Law and Charles’ Law, we get the combined gas law equation.

• P1 V1 and T1 apply to one set of condition, P2 V2 and T2 apply to a second set of conditions.

Joseph Louis Gay-Lussac

• Gay-Lussac’s Law can be restated to: When gases react with each other, the ratio of their reacting volumes is the same as the ratio of their reacting molecules.

Amedeo Avogadro

• At a constant pressure and temperature, the volume a gas occupies is directly proportional to the number of molecules (or number of moles) of the gas that’s present.

• This is the same Avogadro who gave us Avogadro’s number

Demonstrating Avogadro’s Law

• Blow into a balloon (increase the value of n) and

the balloon gets larger (the value of V increases).

John Dalton

• The total pressure of all the gases in a mixture of several gases is the sum of the pressures exerted by each of the individual gases -- the sum of their individual partial pressures.

The Partial Pressures of the Air We Breathe

• Notice that the sum of these partial pressures is 760 mm-Hg, which is our standard atmospheric pressure.

William Henry

• If the partial pressure of a gas above a liquid is low, very little of the gas dissolves in the liquid.

• If the partial pressure of a gas above a liquid is high, plenty of the gas dissolves in the liquid.

• We can describe the concentration of the dissolved gas in the liquid by using the partial pressue of the gas above the liquid.

The Laws of a Bottle of SodaPart I

The Laws of a Bottle of SodaPart II

The Art and Science of Breathing

• We metabolize glucose (and other nutrients) for energy.

• Body cells require O2 as a reactant.

• Body cells produce CO2 as a product.

• Our blood must supply oxygen and remove carbon dioxide.

• The gas laws come into play in the process.

The Physiology of the Lungs

Blood Transports O2 and CO2 Between the Alveolae and the

Cells

Partial Pressures of Blood Gases

End - Chapter 12