# Lect02 - Physics 213 Lecture 2 Ideal Gases Energy Work and...

This preview shows pages 1–8. Sign up to view the full content.

Physics 213: Lecture 2, Pg 1 Ideal Gases: Energy, Work and Heat Ideal Gases: Energy, Work and Heat Thermal reservoir Physics 213 Physics 213 … Lecture 2 Lecture 2 http://intro.chem.okstate.edu/1314F00/Laboratory/GLP.htm increasing T Volume Pressure c First Law of Thermodynamics - internal energy - work and heat References for Lecture 3 and 4: Elements Ch 3,4A-C and 5 Topics

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Physics 213: Lecture 2, Pg 2 Last time: The Ideal Gas Law Last time: The Ideal Gas Law c Together give us the Ideal Gas Law : 2 3 TRANS N p KE V = ( 29 2 2 2 3 1 2 2 TRANS x y z KE m v v v kT = + + = NkT pV = c The Pressure-Energy relation we derived: c Plus the Equipartition Principle (1/2 kT per quadratic DOF): Later, we will find that this law follows very directly from the definitions of an ideal gas and of T
Physics 213: Lecture 2, Pg 3 c For an ideal gas at constant T, p is inversely proportional to the volume: Ideal gas p Ideal gas p -V, p V, p -T diagrams T diagrams V NkT p = increasing T Volume Pressure Real gases may obey more complicated equations of state, but still two of these variables determine the third. Ordinary gases are often quite close to ideal. p vs. V at various constant T’s ISOTHERMS 0 Temperature 0 “Constant Volume Gas Thermometer” Pressure drops toward zero at absolute zero temperature as the thermal kinetic energy of the molecules vanishes. p vs. T at constant V This relation holds Independently of the internal modes of the molecules.

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Physics 213: Lecture 2, Pg 4
Physics 213: Lecture 2, Pg 5 Consider a fixed volume of an ideal gas. If you double either T or N , p goes up a factor of 2. ( pV = NkT ) If you double N , how many times as often will a particular atom hit the container walls? (A) × 1 (B) × 1.4 (C) × 2 (D) × 4 ACT 1: Ideal gas behavior

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
Physics 213: Lecture 2, Pg 6 Dalton’s Law of Partial Pressures for ideal gases If a gas has multiple components (e.g., 78% N 2 , 21% O 2 , etc.), the total pressure is the sum of the individual partial pressures: p total = p 1 + p 2 + p 3 +… Example: Since air is 78% N 2 (by number , not by weight), the partial pressure of the nitrogen component is just 0.78 x 1 Atm. To get pV=NkT, we never used that the molecules were all of the same type. Equipartition makes the contribution of a molecule to the pressure independent of its mass. All that matters is how many molecules there are.
Physics 213: Lecture 2, Pg 7 c “Classical” means Equipartition Principle applies: in thermal equilibrium, each molecule has average energy ½ kT per quadratic mode Internal Energy of a Internal Energy of a Classical Classical ideal gas ideal gas And we define (for 213) And we define (for 213) α α -ideal gases ideal gases V p T k N U α = α = c For a classical ideal gas: ( α depends on the type of molecule ) At room temperature, for most gases : T k N U 2 3 = monatomic gas (He, Ne, Ar, …) 3 translational modes (x, y, z) T k N U 2 5 = diatomic rigid molecules (N 2 , O 2 , CO, …) 3 translational modes (x, y, z)

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

## This note was uploaded on 09/12/2009 for the course PHYS 214 taught by Professor Debevec during the Spring '07 term at University of Illinois at Urbana–Champaign.

### Page1 / 36

Lect02 - Physics 213 Lecture 2 Ideal Gases Energy Work and...

This preview shows document pages 1 - 8. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online