Temperature and Kinetic Theory

1. Temperature and Kinetic Theory Chapter 13

2. Atoms and Molecules • 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

3. Atomic Theory of Matter • On a microscopic scale, the arrangements of molecules in solids (a), liquids (b), and gases (c) are quite different.

4. 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

5. 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.

6. 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.

7. Temperature • In everyday life temperature might be measured in Fahrenheit or Celsius • To convert between F and C • ْF= 9/5 ْC + 32 • The SI unit of temperature is kelvin (K) • To convert between K and C • K=ْC+ 273.15

8. 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

9. 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

10. 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

11. 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:

12. Molecules & Avogadro’s Number • The number of molecules in one mole is the same for all gases. • That number is Avogadro’s number

13. The Ideal Gas Law • Where n is the number of moles • Ris the universal gas constanthas 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

14. Real gases and Changes of Phase . • Aphase (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

15. Phase diagram of carbon dioxide • The triple point is the only point where all three phases can coexist in equilibrium.

16. Diffusion • Even without stirring, a few drops of dye in water will gradually spread throughout. This process is called diffusion.

17. . • Diffusion occurs from a region of high concentration towards a region of lower concentration

18. References • 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