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Temperature and Kinetic Theory

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# Temperature and Kinetic Theory - PowerPoint PPT Presentation

Temperature and Kinetic Theory. Chapter 13. Atoms and Molecules. A tomic 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 )

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## Temperature and Kinetic Theory

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### Temperature and Kinetic Theory

Chapter 13

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

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
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
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
• 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
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
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
• 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