Ma PChem 8/26, 8/28, 8/31, 9/2, 9/4
Ma PChem 8/26, 8/28, 8/31, 9/2, 9/4 CHEM 345
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This 4 page Class Notes was uploaded by Kayli Antos on Saturday September 5, 2015. The Class Notes belongs to CHEM 345 at Towson University taught by Dr. Ma in Summer 2015. Since its upload, it has received 68 views. For similar materials see Physical Chemistry in Chemistry at Towson University.
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Date Created: 09/05/15
Physical Chemistry Ma Fall 20 391 Introduction gt Thermodynamic System J J The system is the part of the universe that we re interested in studying An open system is one that can exchange energy and matter across boundaries A system is closed when it can exchange energy but not matter A system is considered isolated when it cannot exchange energy nor matter The surroundings are everything not in the system The boundary is what is between the system and its surroundings This can be real or imaginary xed or moveable gt State Of A System J 9 Any measureable quantities characterizing a system are called its properties Extensive properties are those that are proportional to the mass in a system Intensive properties are independent of mass The combination of certain variables like mass identity state temperature pressure and volume together make up the physical state of a system In order to classify a system you must know the identity amount temperature pressure and volume How variables are reliant on each other in the equation of a state 1 Gas La WS gt The Ideal Gas Gas molecules have a mass so low that it is negligible The molecules do not interact attract or repulse each other Ideal Gas Equation PV 2 nRT Variables with SI unitsnon SI units P Paatm V m3L n mol T K R gt 314 K 1 mol 1008206 L atm K391 mol39l A bar on top of the variable indicates that it is the molar value for example I7 is molar volume You can nd the molar value by dividing the value by the number of moles Molar values can be found for any gas not just ideal gasses The SATP conditions Standard Ambient Temperature and Pressure are T25 C29815K P1bar105 Pa The STP conditions Standard Temperature and Pressure are T0 C27315K P1bar105 Pa gt Real Gas J J There are interactions between molecules They have a compression factor which measures compressibility It is represented as Z Under the same conditions the compression factor is equal to the molar volume of the real gas divided by the molar volume of the ideal gas For ideal gasses Z 1 When Z lt 1 the gas is easy to compress The gas is more dif cult to compress when Z gt 1 This is due to the repulsive interactions being stronger than the attractive interactions gt The Virial Equation Real Gas Equation J J J J Z 15 Z V V V 1 is the rst virial coef cient B C and D are the second third and fourth virial coef cients RT B c D Can rearrange equatlon so 1t 1s P n 1 n 71 2 71 3 V V V V gt The van der Waals Equation for Real Gasses J J J Molecules in a real gas have volume that can be felt by other molecules and lead to repulsion V nbP nRT The attraction of molecules to each other will lead to a reduction in the pressure of the system nRT a n2 V nb V2 2 That equation can be rearranged to read as P a V nb nRT p In these equations a and b are van der Waals parameters Their SI units are Pam6mol 2 for a and m3mol 1 for b Their non SI units are atmLZmol z and Lmol 1 respectively The van der Waals equation can be written with molar volume as PI72 bRT gt Condensation Of Gases J J For an ideal gas at low temperatures the pressure and volume are low At high temperatures the pressure and volume are high Real gasses have a critical point which is where liquids and gasses of a substance coexist at the same temperature Only real gasses can be condensed and can be so below the critical point Above the critical point real gasses can be treated as ideal gasses 391 Kinetic T beOIy 0f Gases gt The Kinetic Model Of Gases J J J Gasses are made up of many atoms that are separated by distances which are very large in relation to their size Molecules have mass but negligible volume The gas molecules are in constant random motion There are collisions between molecules and other molecules and between molecules and the walls of the container These are elastic which means that no kinetic energy is lost as heat or other forms of energy There are no attractive or repulsive forces between molecules gt The Pressure Of Gas J J va2 the 3V W in this equation is the mean velocity squared and is found by squaring The pressure of a gas with N molecules can be expressed as P the velocity of every molecule and dividing by the number of molecules ltEtransgt is the average transitional kinetic energy of one molecule gt Kinetic Energy And Temperature J J J J For an ideal gas PV 2 Etmns nRT That can be rearranged to show Etmns EKBT KB is the Boltzmann constant whose value is 1381 X 10 26 JK For real gasses E KBT gt The Maxwell Distribution Law J J J Ms2 dN W515 3 M 4n Z 526 N ZnRT dNN is the fraction of molecules that are moving at speeds between s and sds If s is small the s2 term dominates the equation If the s is large the 6 term dominates the equation ZRT Most probable speed Smp 7 8RT Average speed S n M 3RT Root mean square speed vrms M O 1 Molecular Collisions gt The Collision Frequency Zi J This is the average number of collisions made by a molecule over a given time period 2 21 mam L V In the above equation NA is Avogadro s Number gt Mean Free Path A V The average distance that a molecule travels between successful collisions is called the mean free path 1 V RT A S zi ndZN ndZPNA V Z is measured in s39l A is measured in m
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