temperature and kinetic theory

Temperature and Kinetic Theory

Chapter 13

1

Atoms and Molecules

2

Atomic theory says that matter is made of atoms; Greek for indivisible

To discuss the relative mass of atoms and molecules we need a unit

This unit is called unified atomic mass units (u) or atomic mass unit (amu)

Based on carbon-12

Atomic Theory of Matter On a microscopic scale, the arrangements of

molecules in solids (a), liquids (b), and gases (c) are quite different.

3

Kinetic-molecular theory Explains the properties of an ideal gas

Says that particles in a gas are in random motion at high speeds

Gas particles undergo perfectly elastic collisions

Gas particles hit each other and/or container and rebound, resulting in pressure on the surface

Theory explains the properties of an ideal gas, which is an accurate model of real gases under most conditions

4

Temperature Temperature is a measure of how hot

or cold something is.

The average translational kinetic energy of the molecules in an ideal gas is directly proportional to the temperature of the gas.

Most materials expand when heated.

5

Thermal Equilibrium and the Zeroth Law of Thermodynamics

Two objects placed in thermal contact will eventually come to the same temperature. When they do, we say they are in thermal equilibrium.

The zeroth law of thermodynamics says that if two objects are each in equilibrium with a third object, they are also in thermal equilibrium with each other.

Temperature

7

In everyday life temperature might be measured in Fahrenheit or Celsius

To convert between F and C 7F= 9/5 7C + 32

The SI unit of temperature is kelvin (K)

To convert between K and C K= 7C + 273.15

The Gas Laws

Boyle’s Law - for a fixed sample of gas at constant temperature, the volume of the gas varies inversely w/ the pressure.

P1V1=P2V2

8

Charles’s Law – under constant pressure, the volume of a sample of gas varies directly with its Kelvin temperature

Guy-Lussac’s Law-at constant volume the absolute pressure of a gas is directly proportional to the absolute temperature

9

We can combine these…

Combined Gas Law – for a fixed amount of an ideal gas, the pressure times the volume divided by the Kelvin temperature equals a constant

10

Moles A mole (mol) is defined as the number of

grams of a substance that is numerically equal to the molecular mass of the substance:

1 mol H2 has a mass of 2 g

1 mol Ne has a mass of 20 g

1 mol CO2 has a mass of 44 g

The number of moles in a certain mass of material:

Molecules & Avogadro’s Number The number of molecules in one mole

is the same for all gases. That number is Avogadro’s number

The Ideal Gas Law

Where n is the number of moles R is the universal gas constant has a

value of 8.314 J/mol·K. In the real world, this ideal gas law

predicts gas behavior well, except under conditions of high pressure or low temperature

.Real gases and Changes of Phase A phase (PT) diagram shows all three phases

of matter • Solid-liquid transition is melting or freezing

• Liquid-vapor transition is boiling or condensing

• Solid-vapor transition is sublimation

Phase diagram of carbon dioxide

The triple point is the only point where all three phases can coexist in equilibrium.

Diffusion Even without stirring, a few drops of

dye in water will gradually spread throughout. This process is called diffusion.

. Diffusion occurs from a region of high

concentration towards a region of lower concentration

References

18

Zitewitz. Physics: Principles and Problems. 2004

Giancoli, Douglas. Physics: Principles with Applications 6th Edition. 2009.

Images http://

missbakersbiologyclasswiki.wikispaces.com/file/view/diffusion.gif/31772061/diffusion.gif