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Unformatted text preview: Ideal-Gas Equation PV = nRT nRT
Know how to solve this equation for any one of the variables if the other 4 are known. The Know constant of proportionality is known as R, the gas constant. Know the most commonly used the values of R. values The density equation is used to find the molecular mass of a gas: PΜ d= RT
It is rearranged to: d • R •T Μ= P Dalton’s Law of Partial Pressures
The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were The total sum present alone. In other words: present Ptotal = P1 + P2 + P3 + … A gas collected over water, contains water vapor mixed in with the gas. To find only the pressure gas contains of the gas, the vapor pressure of water must be subtracted from the total pressure. subtracted total Kinetic-Molecular (KM) Theory
KM theory is a model that aids in our understanding of what happens to gas particles as environmental KM conditions change. conditions Assumptions of KM Theory: Gases consist of large numbers of molecules that are in continuous, random motion. The combined volume of all the molecules of the gas is negligible relative to the total volume in which The the gas is contained. the Attractive and repulsive forces between gas molecules are negligible. Energy is transferred between individual molecules during collisions If T remains constant, the average kinetic energy of the molecules does not change with time. If average Prediction of Kinetic-Molecular Theory:
Average kinetic energy of molecules is directly proportional to the absolute temperature Average directly absolute 0.4
Probability of Probability molecules with given velocity given 0.3 0.2 0.1 0 500
Molecular velocity (meter/sec) 1000 Definition of Effusion: The escape of gas molecules through a tiny hole into an evacuated space. Real Gases The behavior of real gases only conforms to the ideal-gas equation at relatively high T and low P. The Deviations from Ideal Behavior: The assumptions made in the kinetic-molecular model break down at high pressure and/or low temperature. high Corrections for Nonideal Behavior
The ideal-gas equation can be adjusted to take these deviations from ideal behavior into The account. account. One corrected ideal-gas equation is known as the van der Waals equation. The van der Waals Equation for 1 mole:
The ideal-gas equation can be adjusted to take these deviations from ideal behavior into The account. account. One corrected ideal-gas equation is known as the van der Waals equation: a (P + 2 ) (V - b) = RT RT V
This equation includes the effect of: This Attractive forces between molecules and and The volume occupied by the molecules The The van der Waals Equation for 1 mole: a (P + 2 ) (V - b) = RT RT V
Values of a and b parameters for common gases Values ...
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- Spring '08