Chem I chp 6 - Chapter 5 Gases Principal Assumptions of the Kinetic-Molecular Theory 1 A gas is made up of molecules that are in constant random

Chem I chp 6 - Chapter 5 Gases Principal Assumptions of the...

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Chapter 5 Gases
Principal Assumptions of the Kinetic-Molecular Theory 1. A gas is made up of molecules that are in constant, random, straight-line motion 2. Molecules of a gas are far apart – i.e., a gas is mostly empty space 3. There are no forces between molecules except during the instant of collision EOS 4. Individual molecules may gain or lose energy as a result of collisions; however, the total energy remains constant
Examples of Pressure Units Given these values, one can generate conversion factors to switch between units: e.g., 760 mmHg = 1.01325 bar EOS mmHg bar or bar mmHg 760 01325 . 1 01325 . 1 760
Barometers Used to measure atmospheric pressure The pressure exerted by a column of mercury exactly 760 mm high is defined as 1 atmosphere (atm) EOS Gases tend to settle under the effects of gravity – pressure as altitude
Pressure-Volume Relationship: Boyle’s Law For a given amount of a gas at constant temperature, the volume of the gas varies inversely with its pressure i.e., if V , then P EOS
Pressure-Volume Relationship Boyle’s Law P
Temperature-Volume Relationship: Charles’s Law The volume of a fixed amount of a gas at constant pressure is directly proportional to its Kelvin temperature i.e., if V , then T or V/T = k EOS
Temperature-Volume Relationship: Charles’s Law Absolute zero is the temperature obtained by extrapolation to zero volume EOS Absolute zero on the Kelvin scale = –273.15 ° C and ... 273.15 K = 0 °C
Avogadro’s Law: Mole-Volume Relationship
Molar Volumes and Standard Pressure and Temperature S tandard T emperature and P ressure ( STP ) is defined as T = 0 o C and P = 1 atm EOS The molar volume of a gas is the volume occupied by one mole of the gas at STP
The Combined Gas Law Given the various gas laws, all can be combined into a single form … V = k/P , V = kT , and V = kn V ( nT )/ P k nT PV For initial and final conditions: EOS 2 2 2 1 1 1 nT V P k nT V P

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