1 / 19

Chapter 10 - PowerPoint PPT Presentation

Chapter 10. Temperature and Kinetic Theory. Definitions. Temperature – a measure of the average kinetic energy of the the molecules making up a substance, measured in [C] or [F] or [K].

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

PowerPoint Slideshow about ' Chapter 10 ' - evers

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Chapter 10

Temperature and Kinetic Theory

• Temperature – a measure of the average kinetic energy of the the molecules making up a substance, measured in [C] or [F] or [K].

• Internal Energy (thermal energy) the combined kinetic and potential energy of the molecules of a substance measured in [Joules].

• Heat – the transfer of thermal energy measured in [Joules].

Potential energy – when molecules have stored energy

Internal Energy

Fahrenheit and Celsius Scales

Fahrenheit, Celsius and Kelvin Scales

• F = 9/5 C + 32

• C = 5/9(F – 32)

• K = C + 273

• PV = nRT

• P = Pressure

• V = Volume

• n = number of moles

• R = univ. gas constant (8.31 J/mol ºK)

• T = Temperature in Kelvin

• A mole of a substance is a quantity containing 6.02 X 1023 molecules

• Standard Temperature and Pressure means p = 1 atm = 1.01 X 105 Pa,

T = 0ºC = 273 K

• Formula weight in Grams = 1 mole

• Must use Kelvin for temperature!

If the number of molecules (mass) doesn’t change:

• Constant Temperature, then p1V1 = p2V2

• Constant Pressure , then V1/T1 = V2/T2

• Constant Volume, then p1/T1 = p2/t2

• A low density gas in a rigid container is initially at 20ºC and a particular pressure, p1. If the gas is heated to 60ºC, by what factor does pressure change?

• The weather report gives the day’s high temperature as 10ºC and predicts the next day’s high temperature as 20ºC. A father tells his son that this means it will be twice as warm tomorrow, but the son says it does not mean that. Do you agree with the father or the son?

• Solids and liquids expand or contract with changes in temperature.

• Space between molecules becomes greater or less as temperature changes.

• ΔL = αL0ΔT ; L0= original length

α =thermal coefficient of

linear expansion

• A steel beam is 5.0 m long at 20ºC. On a hot day, the temperature rises to 40ºC. What is the change in the beam’s length? α = 12 X 10-6 C-1

• ΔA = 2αA0ΔT Area Expands with Temperature

• ΔV = 3αV0ΔT Volume Expands with Temperature

Macroscopic vs Microscopic Ideal Gas Law

Macroscopic

pV = nRT R = 8.31 J/mol K

n = # of moles

• Microscopic

pV = NkbT kb = 1.38 X 10-23 J/K

N = # of molecules

• Monatomic – single atom gases.

• Diatomic – molecules contain 2 atoms.

• Monatomic gases are easy to study because atoms move without rotation or vibration

• Monatomic gases obey the laws of mechanics (recall for elastic collisions we apply Conservation of Momentum and Conservation of Energy)

Molecules (atoms) undergo perfectly elastic collisions with the walls of the container.

We assume molecules are separated by large enough distances so that molecular collisions can be neglected.

Then…

pV = 1/3 Nmv2rms

N = # of molecules

m = mass of molecule

vrms = average speed of molecule

Kinetic Theory for Monatomic Gases

Math… the walls of the container.

pV = 1/3 Nmv2rms = NkbT

So ½ mv2rms = 3/2 kbT

Or 3/2 kbT = ½ mv2rms

What does this mean?

Temperature is proportional to average KE!

Example the walls of the container.

• Find the average speed (v2rms) of a Helium atom in a 20ºC balloon at room temperature. Assume

mHe = 6.65 X 10-27 kg

Summary- Kinetic Theory for Monatomic Ideal Gas the walls of the container.

Average Kinetic Energy

• KEav = ½ m vrms2 = 3/2 kbT

kb = 1.38 X 10 -23 J/K

Total Internal Energy

• U = 3/2 NkbT = 3/2 nRT