Thermod Chapter3 Ideal Gas.Pdf

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Energy revisited …
From the molecular view there exist three general view, forms of energy:

Intermolecular Potential energy: It is associated with the forces between the molecules. Molecular Kinetic energy: It is associated with the translational velocity of individual molecules. Intramolecular energy: It is associated with molecular and atomic structure and related force 2

Low Density Gas
• A At very l low d densities, the ii h average distances between molecules are very l l l large and d intermolecular potential energy can b neglected. be l d • In such cases, particles are independent of each other - this is referred to as an Ideal Gas.

Ideal Gas Equation of State
• The simplest and best known equation of state for substances in the gas phase is the Ideal gas Equation of State.

Pv

R T

The universal gas constant

R

RM 8.3145 kJ / kmol K 1545 ft lbf / lbmol R f f

M = Molecular weight, kg/kmol kg/kmol /

Ideal Gas Equation of State PV = mRT Pv = RT
• The gas that obeys this relation is g y called an Ideal Gas. • Where R (Gas constant) is different constant for each particular gas gas. • The value for R for a number of substance is given in Table A 5 A.5

Ideal Gas Equation of State
• Because of being simple simple, ideal gas equation is used in thermodynamic calculations, wherever possible. • It is applicable to actual gases at low density. • At low pressure and high temperature, the density of gas d d it f decreases and gas b h d behaves as an ideal gas under these conditions

Non-Ideal or Real Gas
•Low Temperature •High P Hi h Pressure •Particle size significant compared to space between particles ti l Interactions •Interactions between particles are significant

Ideal Gas Equation of State
• At low pressure and high temperature the temperature, density of gas decreases and gas behaves as an ideal gas under these conditions conditions. • Over what range of density Ideal Gas Equation of Sate hold with accuracy? • How...
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