Molecular Properties of Gases
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Equation of state for a real gas: |
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The ideal gas equation is given by,
PV=nRT
Where P= pressure exerted by the gas molecules on the walls of the container, V= volume of the
container, n= number of moles of the gas, R= universal gas constant, and T= Temperature of the
gas in Kelvin. This equation is not valid for a real gas. Thus, further considerations are taken. If
every mole of the particles of the gas has a tiny finite volume of b,
with n moles of molecules this
makes a total amount of (b.n). This amount has to be subtracted from the overall volume V, hence
the term (V-b.n) will be there in place of V. Now, the other modification is due to the particles
sticking to each other, a phenomenon called cohesion. This sticking is proportional to (n/V)2 and it
reduces the effective measured pressure P. For that reason it must be compensated for in the
formula by adding the term a•(n/V)2 to the pressure. Thus, the ideal gas equation in modified form
would be:
This equation is valid for real gases and is called van der Waals equation.
The intermolecular forces:
covalent compounds.
- Ionic Compounds: The ionic compounds basically show the electrostatic forces existing in between the charges species and are responsible for the extremely high melting and boiling points of ionic compounds
- Covalent Compounds: In the covalent compounds there are basically three types of forces seen in nature
- London forces - all molecules have the capability to form London forces. These are solely dependent on the surface area and the polarizability of the surface of the molecule. These are the only types of forces that non-polar covalent molecules can form. They result from the movement of the electrons in the molecule which generates temporary positive and negative regions in the molecule
- Dipole-dipole forces - only polar covalent molecules have the ability to form dipole-dipole attractions between molecules. Polar covalent molecules act as little magnets; they have positive ends and negative ends which attract each other.
- Hydrogen bonding - these occur between polar covalent molecules that possess a hydrogen bonded to an extremely electronegative element, specifically
- N, O, and F
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